Backgrounds and themes are two different things; you have one of each. Classes and races may suggest themes, but you can choose any.

• "Our current plan is to condense skill and feat choices into two choices: background and theme. Background tells you where you came from, who you were, and what you are trained to do. Your background gives you a set of skills, specific tasks, areas of knowledge, or assets a character of that background ought to have. The thief background gives you Pick Pockets, Stealth, Streetwise, and Thieves’ Cant. The soldier background gives you Endurance, Intimidate, Survival, and an extra language. We want your abilities to carry the weight of basic task resolution, so these skills improve your chances when you perform tasks related to them or just let you do something, such as cook a meal, speak Goblin, or run for twice as long as the next person. Where background speaks to the skills you possess, your theme describes how you do the things you do. All fighters, for example, kick ass in combat because they are fighters. A sharpshooter fighter is awesome with ranged weapons while a slayer fighter dominates in hand-to-hand combat. Your theme helps you realize a certain style, technique, or flavor through the feats it offers. Each theme gives you several feats, starting with the first one right out of the gate. As you gain levels, your theme gives you additional feats that reflect the theme’s overall character." - Monte Cook.
  

• Themes cover potion-makers and blacksmiths. Like kits from 2E. You can improve in that theme with feats etc. Or you can use skills and feats to customize your own theme.
  
• Themes such as commoner, noble, knight, apprentice. Also planetouched, deva, avenger. There is one called "pub crawler". So you can have an avenger themed paladin.
  
• Themes tie into open-ended skill system - skills for specific themes.
  
• [NEW 20 APRIL] Robert Schwalb's blog entry Backgrounds and Themes: A Closer Look is packed with information:
  
  • "Your class will suggest a theme, but we expect you to choose whatever theme you like. The suggested theme for a fighter might be Slayer, while the suggested theme for a wizard might be Mystic."
    
  • "The theme you gain at 1st level isn’t the only theme you get. ... The first theme you choose is broadly descriptive and flexible. Think Leader, Sharpshooter, or Skirmisher. When you adopt your second theme at 6th level, you might choose another basic theme or you might choose something that grounds you a bit more in the game by selecting an advanced theme. Currently, advanced themes, in concept, resemble the prestige classes from 3rd Edition.... A Sharpshooter becomes an Arcane Archer. A Tempest becomes an Eldritch Knight. A Lurker becomes a Shadowdancer. A Mystic becomes a Necromancer or Enchanter or Abjurer. A Slayer becomes an Axe Specialist. A Guardian becomes a Dwarven Defender."
    
  • 1st-level Themes mentioned: Slayer, Mystic, Guardian, Lurker, Leader, Sharpshooter, Skirmisher, Tempest, Weapon Master, Wild Talent, Domain Themes, Avenger, Werewolf, Revenant, Disciple of Tenser, Alchemist, Red Wizard, Commoner, Noble, Knight, Apprentice, Planetouched, Deva, Pub-Crawler, Spy
    
  • 6th-level themes mentioned: Arcane Archer, Eldritch Knight, Shadowdancer, Necromancer, Enchanter, Abjurer, Axe Specialist, Dwarven Defender
    
  
  
• [NEW 1 MAY] "The design right now delivers feats through themes—so yes, themes are the delivery device, just as themes in Dark Sun are a delivery device for some powers." - Rodney Thompson.
  
• [NEW 15 MAY] "Races are a little different, because we can imagine that there are some themes that tie in well to the race's culture. For example, we might do a dwarven defender theme, or an elven bladesinger theme, which would tie into race as a cultural touchstone, but probably wouldn't tie in especially tightly to that race's mechanics." - Rodney Thompson.
  

From Backgrounds and Themes: A Closer Look:

• Backgrounds mentioned: Gladiator, Bureaucrat, Awakened (psionic), Priest, Occultist, Commoner, Bereaved, Sage, Knight of the Watch, Blackmoor, Thay, Harper, Dustmen, Fated, Hamonium, Thief, Soldier
  
• "We will still suggest backgrounds in each class so people who want the implied background commonly associated with classes can use them. But, by giving players the option to swap out one set of skills for another, to swap out individual skills for other individual skills, or to construct a set of skills to match the player’s character concept, we can shade classes in any way we want without having to introduce new subclasses beyond the classic concepts (ranger, paladin, druid, and so on) or put unwanted pressure on multiclassing to deliver these same results."
  
• Party Backgrounds: "I’ve been thinking about party backgrounds as an optional system. Players might choose a background for their character and then get a bonus skill from the party list (mercenaries, thieves, pilgrims, cult). The party background might also reward characters who have the same skills."
  
• Backgrounds are the primary skill delivery mechanism. Skills are generally divorced from class, and backgrounds all offer a roughly equal number of skills. - Rodney Thompson.
  
• [NEW 16 MAY] "As it currently stands, your background grants you four things—either skills or traits. A skill always refers to a specific task: climbing, charm, deception, and so on. If you have training, you get a +2 bonus to any check made that involves that task. The bonus typically increases based on your class (rogues are good with skills) or, if you gain training in the skill again, increasing the bonus by 1 for each instance." -Robert Schwalb.
  

[NEW 15 MAY] Traits are another level of character background detail.

• "We imagine that traits cover a pretty broad swath of different abilities, mostly tied to your character's unique history. A simple expression of this would be a few extra languages, which opens up more roleplaying possibilities for the character. A more specialized trait would be one that allows a knight to always be able to get lodging and aid from a noble house that recognizes his or her own noble claim." - Rodney Thompson.
  
• From this column by Robert Schwalb:
  
  • Where skills can improve your chances for success in specific situations, traits are minor benefits that usually interact with specific tasks. A trait doesn’t grant you a bonus. It just lets you do something or speaks to your character’s place in the world. Here are two example traits:
    
    • Extra Language: You are fluent in a language of your choice.
      
    • Workshop: You own a workshop somewhere in the world. Work with your DM to determine the best possible location for this shop. You have everything you need to produce the items you have learned to craft.
      
    
    
  
  

• [NEW 21 MAY] Hit Dice: d10
  
• Fighter was the hardest class to design. Druid second hardest. Monk easy.
  
  • "The fighter is also the class that supports the broadest spectrum of archetypes, from swordsman to archer." - Rodney Thompson.
    
  • "I will say my Fighter was +X to hit, rolled dice a lot" - Dave C. of Baldman Games (which runs DDXP); this appears to confirm that + to hit remains, as opposed to some other mechanic.
    
  • "So for example, if your fighter goes up a level and would normally get some bonus damage or a bonus to hit, or something simple, then maybe instead you could choose to replace that with an option or options that allow you to do some cool moves that allow you to push people around, or protect your allies a bit more, or control the battlefield a little more."
    
  • Fighters have their version of abilities and options as well, but it will have a different feel than the Vancian magic for arcane stuff.
    
  • Monte Cook: "For example, the basic game fighter might have specific level-bases abilities. Things that every fighter has. If you decide to get more customized, you can swap standard abilities for more complex, optional abilities. These are the kinds of things that feats do now. But the complex stuff is balanced with what's in the core. One character is more complex, but not necessarily more powerful."
    
  • "...in several editions the fighter's primary mechanics are tightly tied to subsystems that, in the upcoming iteration of D&D, might be optional or even absent. The 3rd edition fighter gets a lot of bonus feats, but what if feats were an optional subsystem? The 4th edition fighter derives much of its mechanics from the powers system; what would the fighter look like if powers were optional? In 4E, the fighter would be left with marking or defender aura, but I would argue that the fighter's defender mechanics are representative of a play style that should be available to many different character archetypes, and not be the sole province of the fighter." - Rodney Thompson.
    
  • "Instead of the fighter getting a better and better attack bonus, he instead gets more options to do stuff as he goes up in level, and his attack bonus goes up at a very modest rate." - Monte Cook.
    
  • "For example, the fighter might be concerned with things like the preservation of hit points, which not only includes making strategic choices at character creation, but also might involve managing a pool of self-healing resources, or using defense-based options to mitigate damage while still occupying an enemy's attention (thus also mitigating the damage that enemy could do to the fighter's allies)." - Rodney Thompson
    
  • "I mentioned that the fighter could serve the need for a low complexity class, and also have options to serve the needs of those who want a high complexity class." - Rodney Thompson
    
  • "For example, if you substitute maneuvers in for individual attacks, the fighter class plays more like a mix-and-match system combining maneuvers and multiple attacks; on my turn, I charge the orc, then use my next attack to disarm him, and my final attack to push him back away from the weapon he dropped." - Rodney Thompson.
    
  • "...our current vision for both the fighter and the rogue includes access to a system of combat maneuvers." - Rodney Thompson.
    
  • "...instead of the fighter having to spend a single action to make multiple attacks, we might say that the extra attacks that the fighter gains as he gains levels are effectively free actions that the fighter takes on his turn." - Rodney Thompson
    
  
  

[NEW 30 APRIL] Mike Mearls talks about the fighter's design goals here.

• The fighter is best at... fighting!
  
• The figter draws on training and experience, not magic
  
• The figher exists in a world of myth, fantasy, and legend
  
• The figher is versatile
  
• The fighter is the toughest character
  
• A high-level fighter and a high-level wizard are equal
  

• Psion, wild talents exist.
  

• Barbarian: fits with what some of us are familiar with, he rages and can take lots and lots of damage and deal out lots of damage.
  

• [NEW 21 MAY] Hit Dice: d8
  
• Cleric: has an interesting mix of healing and other options. Cleric getting back to the cleric of 1E that fights with a mace and shield and gets his party back up.
  
  • Core is Vancian (like Wizard).
    
  • "I don't think 'requiring someone to be a healer' is a sacred cow, but having healers in the game is. I wouldn't want to see D&D do away with healing, but I don't think there's anything keeping us from exploring a version of D&D where players can simply play anything they want, ignoring concepts like role and function when putting together their party. To do so, we would need to take a serious look at the way player resources are allocated in D&D, and make some adjustments to the assumptions behind the design of everything from adventures to encounters to monsters." - Rodney Thompson.
    
  • "...the cleric was very, VERY adept at stabilizing people, like, move-attack-YOUARENOTDYING good at it." [source]
    
  • "Seemed like standard low-level 2e/3e fair, cure wounds, bless, etc. Nothing huge, fancy, or off-the-wall." [source]
    
  
  
• Domains
  
  • [NEW 21 MAY] "Our new take on domains moves a little closer to spheres in intent." - Mike Mearls.
    
  • [NEW 19 JUNE] "Cleric domains represent a baseline choice that clerics make that flavor many of the abilities they gain. First of all, much like spheres in 2nd Edition, the cleric's choice of domain opens up new options for the spells that cleric can prepare each day. Second, the cleric's choice of domain grants some baseline class features that alter how the character plays; for example, the cleric who chooses the War domain gains proficiency in heavy armor and shields, while the cleric who chooses the Sun domain gains resistance to radiant damage. At higher levels, the cleric's domain choice helps provide more powerful class features that form an integral part of the cleric's play style; again, as an example, the War domain cleric might gain the ability to cast a spell and make a melee attack as a single action, while the Sun domain cleric could get a free radiant lance spell once per round." - Rodney Thompson.
    
  
  

[NEW 23 APRIL] Mike Mearls summarizes the cleric's design goals in this article on DDI:

• The cleric is a healer
  
• The cleric is a divine spellcaster
  
• Divine magic is subtle and indirect
  
• The cleric is an armored warrior
  
• Clerics reflect the gods
  

"You can imagine having a set of healing spells that allow you to aid your allies while still attacking, while also having different spells that take your entire turn. As a player, you can decide to focus on serving as a healer, choose to straddle the middle ground between fighting monsters and helping your allies, or even opt to pick spells such as bless or lance of faith and then emphasize the warrior aspect of your character."

• Mike Mearls discusses turning undead in this column: "When a cleric attempts to turn the undead, he or she makes a Charisma check (presumably with a bonus based on cleric level—maybe +1 per 2 levels?). All the undead within a 30-foot cone in front of the cleric are subject to the turn attempt. Each undead creature has a turn DC embedded in its description. If the cleric succeeds against a creature, the creature suffers the effects described alongside its turn DC. If the check fails, the cleric's attempts to turn that specific creature automatically fail for the next 24 hours. This approach places the effects related to a turn attempt within the individual creature's description, which allows DMs and designers to determine what happens when you turn a specific type of undead monster."
  
• "I like the literal idea of turning, as in turning away the undead from the cleric rather than blasting them with holy energy." - Mike Mearls.
  

• Warlord: "The one we saw was very charisma-based, lowish strength, but very 4e in basic function; initiative bonuses and granting free attacks to others that did extra damage, presumably by pointing out how very stabbable faces are." [source]
  

• [NEW 21 MAY] Hit Dice: d6
  
• Wizard: Vancian magic is core. Other options for other classes, but wizard and cleric are Vancian.
  
• Six spells per level are available in the "basic" game, starting off. (The number of spellslots per level remains unknown). - D&D Podcast
  
• Wizards have magical feats that are basically at will abilities. Wizards have magical feats (at-will, always available). Hold on to higher spells until needed.
  
• Fireball is a static 5d6. If you want more damage, you use a higher-level spell slot.
  
• "...there's no reason why, in addition to Vancian spellcasting for wizards and other classes, we couldn't explore alternatives. If we've done our job right, we can provide rules for spell points or some other spellcasting system, or maybe several other spellcasting systems if we need to. A goal for the game is to make it as modular as possible while still maintaining a baseline of classic D&D fantasy, and part of that modularity can include alternatives to mechanics presented in the baseline. We also know that there are elements of non-Vancian magic systems that would be a good idea to incorporate into a Vancian wizard; at-will spells are a piece of game tech that doesn't fit in the classic Vancian model, but that we know is both popular with players and also helps reinforce the wizard as a representative of the master-of-magic archetype." - Rodney Thompson.
  
• Rituals are there for the really big spells that are super awesome, but might take a bit longer to cast.
  
• Spell Components - limited to rituals only. Rare components as quests.
  
• Feats cover at-will abilities. Wizard has javelin of fire at-will feat ability.
  
• "Magic seems Vancian, with spells leveled 1 to 10. Yes, no 0 spells on the sheet, but the bar clearly went to 10." [source]
  
• "The wizard had some type of at-will magic attack, rinky-dink spell, and a very limited Vancian-style pool of prepared spells. Casting spells was a mishmash of 4e and 3e, opposed attacks vs rolled defense, with the attacker setting the DC with a roll and the defender rolling against that." [source]
  
• "Magic Missile just plain hit. It was either 1d4+1 or 1d6+1 I think, BUT, it was definitely 2 missiles." [source]
  
• "...an at-will scorching ray type deal, some daily magic missile-age, mage armor... the basic stuff really." [source]
  
• "Spell descriptions looked 3e-style" [source]
  
• [NEW 16 May] Cantrips: "...cantrips that you use to attack are basically utility cantrips that have a way you can use them against creatures. The ignite cantrip lets you start fires, whether its lighting a torch or a goblin's butt." - Mike Mearls.
  
• [NEW 21 MAY] Familiars: "It’s a tricky line to walk. A familiar has a clear tie to arcane magic, so we have some flexibility in how we present them. I think we’ll look at how people react to the familiar mechanic to get a sense of how much flexibility we have here. Some people really like the feeling that a companion animal is a flesh and blood creature, but there are a lot of advantages to presenting it as a spirit companion or something similar." - Mike Mearls.
  

[NEW 14 MAY] Mike Mearls discusses the wizard in this article.

• "The challenge lies in making sure that wizards don't grow too powerful as they level. In many campaigns, a caster can use the right combination of spells and magic items to become more powerful than the rest of the group combined."
  
• Cantrips as At-Will Magic: Making cantrips more powerful and useable at-will.
  
• Keep Spells Under Control: Make sure spells aren't too powerful or have powerful loopholes.
  
• Reducing Total Spell Slots: Instead, cantrips are at-will.
  
• Spells Don't Automatically Scale: You need to memorize it in a higher slot.
  
• Spellcasting Is Dangerous: Wizards need protection or to stay out of harm's way while casting.
  
• Keep Magic Items Under Control: There's a good chance that magic item creation will be a rules module that DMs can opt into.
  
  • Scrolls require expending a spell to cast
    
  • Wands have a limited list of spells they can use
    
  
  
• Keep Buff Spells Under Control: Don't let them make other classses redundant.
  
• Creativity, Not Dominance: "I'd love it if creative use of a spell focused more on improvisation rather than number crunching...good, clear descriptions into the spells that bring them to life and combine these descriptions with a robust set of DM tools for improvisation, spells become tools that characters can use in creative ways rather than strictly defined special abilities."
  

• [NEW 21 MAY] Hit Dice: d8
  
• Rogue: "...our current vision for both the fighter and the rogue includes access to a system of combat maneuvers." - Rodney Thompson.
  
• "The rogue in the current playtest document has sneak attack, and it’s a combination of the 3rd Edition and 4th Edition rules. The extra damage as of right now goes all the way up to 10d6 at the highest levels, but a rogue can use the damage against anybody. " - Robert Schwalb.
  
• "If a rogue can't attack from behind or with some other key advantage, he or she might be better off withdrawing or remaining out of sight until the opportunity for a surprise attack presents itself." - Mike Mearls.
  
• "I’m dancing around an idea, so I might as well come out and say it. Here it is: Everyone in the game can backstab. Rogues, if they want, can be the best at backstabbing." - Robert Schwalb.
  
• "We like the idea of rogues and skills being tied together as an aspect of the rogue's identity (but not the totality of that identity). Right now, we're experimenting with giving the rogue extra skills, on top of those that everyone gains, as a way to express that aspect of the class; we may also give the rogue some exclusive skills or skill-like abilities, but that is something we're still working on." - Rodney Thompson.
  
  • "You can never be fully certain of what a rogue might be able to do. If a rogue decides to master a mundane skill, he or she can reach a higher level of expertise than other characters." - Mike Mearls.
    
  • "Traditionally, the mechanics of D&D have reflected better training by increasing the chance of success. That doesn't quite capture the rogue's level of talent. The rogue isn't just more likely to succeed. Instead, he or she takes success for granted in most cases. It's only when facing a real challenge that the rogue must worry about the outcome." - Mike Mearls.
    
  
  
• [NEW 16 MAY] Rogues have "schemes". - Mike Mearls.
  
• [NEW 21 MAY] "Rogues pick a scheme, inspired in part by the 2e mechanic that let thieves allocate points to their skills so that they could focus on one ability or another." - Mike Mearls.
  

[NEW 7 MAY] Mike Mearls discusses the rogue here.

• The rogue doesn't fight fair
  
• Rogues are skilled
  
• The rogue exists in a world of myth, fantasy, and legend
  
• The rogue makes the routine look trivial
  

• The assassin has been mentioned (very briefly) here and here.
  

• [NEW 19 JUNE] Celtic Roots: "The first pass on bards is going back to their Celtic roots while also looking at making a jack of all trades mechanic that doesn't make the bard second best at everything. It's still early, and the final design might be much different, but I really want to give the bard something unique that really speaks to their roots." - Mike Mearls.
  

• The DDI article Paladin Versus Cleric: FIGHT! was writtten before the paladin's design goals were written, and discussed various approaches that might be taken. It also had a poll for visitors to vote on various aspects.
  

[NEW 20 MAY] Mike Mearls discusses the paladin here.

• The paladin is a champion of a divine calling
  
  • Always lawful, but can be good, neutral, or evil
    
  
  
• A paladin can see and smite evil.
  
  • " For instance, although a good paladin cannot unerringly zero in on a specific threat merely by walking past a structure infested with evil, the paladin knows something is wrong."
    
  
  
• A paladin is a fearless and selfless warrior.
  
  • "...nearly as skilled as a fighter and typically armed with heavy armor and a sword, and utterly without fear."
    
  • "...a paladin aspires to find a blessed sword of unequaled power: a holy avenger."
    
  
  
• A paladin has divine abilities.
  
  • "...including the ability to heal allies with a touch (lay on hands), turn undead, perhaps cast a limited number of divine spells, and have at least the option to call a mount."
    
  • "For example, when a paladin calls a mount, that mount might inspire the normal mounts of the paladin’s allies, granting them speed and endurance while they travel together. When a paladin turns undead, he or she can also turn demons, devils, and other unholy creatures. And when a paladin lays on hands, the healing might also relieve malign conditions and spent stamina."