This is an updated list of the films of the Marvel Cinematic Universe in order of internal chronology (not release order); including shorts and other releases (feature films are in bold):

• 
  Captain America: The First Avenger


• 
  Marvel's Agent Carter Season 1


• 
  Marvel's Agent Carter Season 2


• 
  Marvel One-Shot: Agent Carter (short; Iron Man 3 release)


• Iron Man


• 
  The Incredible Hulk (campus rampage; overlaps w/ Iron Man 2)


• Iron Man 2


• 
  Marvel One-Shot: A Funny Thing Happened on the Way to Thor's Hammer (short; Captain America release)


• 
  Thor (reference to Bruce Banner/The Hulk's experiment; overlaps w/ Iron Man 2)


• 
  Marvel One-Shot: The Consultant (short; Thor release)


• 
  Captain America: The First Avenger (end of movie; post credits)


• 
  The Avengers (aka "Avengers Assemble")


• 
  Marvel One-Shot: Item 47 (short; The Avengers release)
  
  
  
  
  • 
    Spider-Man: Homecoming (beginning)
  
  
  
  


• Iron Man 3


• 
  Marvel One-Shot: All Hail The King (short; Thor: The Dark World release)


• 
  Marvel's Agents of S.H.I.E.L.D. Season 1, Pilot (ep. 1) to The Hub (ep. 7)


• Thor: The Dark World


• 
  Marvel's Agents of S.H.I.E.L.D. Season 1, The Well (ep. 8) to End of the Beginning (ep. 16)


• 
  Captain America: The Winter Soldier (runs simultaneously with Marvel's Agents of S.H.I.E.L.D. ep. 16)


• 
  Marvel's Agents of S.H.I.E.L.D. Season 1, Turn Turn Turn (ep. 17) to Beginning of the End (ep. 22)


• Guardians of the Galaxy


• Guardians of the Galaxy 2


• 
  Marvel's Agents of S.H.I.E.L.D. Season 2, Shadows (ep. 1) to The Dirty Half Dozen (ep. 19)


• 
  Marvel's Daredevil Season 1 (covers some indeterminate period between The Avengers and Avengers: Age of Ultron)


• 
  Avengers: Age of Ultron (overlaps w/ Marvel's Agents of S.H.I.E.L.D. ep. 19)


• 
  Marvel's Agents of S.H.I.E.L.D. Season 2, Scars (ep. 20) to S.O.S., Part Two (ep. 22)


• Ant-Man


• 
  Marvel's Jessica Jones Season 1 (early episodes reference Captain America and The Hulk destroying buildings in Age of Ultron; probably on par with Marvel's Agents of S.H.I.E.L.D. season 3)


• 
  Marvel's Agents of S.H.I.E.L.D. Season 3, Laws of Nature (ep.1) to Failed Experiments (ep. 19)


• Daredevil Season 2


• Luke Cage Season 1


• Captain America: Civil War


• 
  Marvel's Agents of S.H.I.E.L.D. Season 3, Emancipation (ep.20) (news report of Captain America's disappearance after the Civil War) to Ascension (ep. 22)


• Marvel's Agents of S.H.I.E.L.D Season 4


• Doctor Strange


• Iron Fist Season 1


• Spider-Man: Homecoming


• 
  The Defenders Season 1

The Official MCU Viewing Order

This is the intended viewing order by Marvel.

• Movies are in bold.


• "One-Shots" are short films included with the home video releases of the films. They frequently tie into the film universe in big ways.


• TV shows are in italics and (according to Marvel) may not be 100% canon with the film universe. (In fact most TV shows are not connected to the film universe in any meaningful way. Their placement does not indicate importance in the overall story.)

Phase One: "Avengers Assembled"

• 
  Iron Man (2008)


• 
  The Incredible Hulk (2008)


• 
  Iron Man 2 (2010)
  
  
  
  
  • One-Shot: "The Consultant" (2011) (4 mins)
    
    Found on Thor Bluray -- set directly after The Incredible Hulk and Iron Man 2
    
  
  
  
  


• 
  Thor (2011)
  
  
  
  
  • One-Shot: "A Funny Thing Happened on the Way to Thor's Hammer" (2011) (4 mins)
    
    Found on Captain America Bluray -- set directly before Thor but makes more sense to watch afterwards
  
  
  
  


• 
  Captain America: The First Avenger (2011)
  
  
  
  
  • One-Shot: "Agent Carter" (2013) (12 mins)
    
    Found on Iron Man 3 Bluray -- set directly after Captain America
    
  
  
  
  


• 
  The Avengers (aka "Avengers Assemble") (2012)
  
  
  
  
  • One-Shot: "Item 47" (2012) (12 mins)
    
    Found on The Avengers Bluray -- set directly after The Avengers
    
  
  
  
  

Phase Two

• 
  Iron Man Three (2013)
  
  
  
  
  • One-Shot: "All Hail The King" (2014) (12 mins)
    
    Found on Thor: The Dark World Bluray -- set directly after (and contains major spoilers for) Iron Man 3
    
  
  
  • 
    Agents of SHIELD (Season 1) - Up until The Hub (ep. 7)
  
  
  
  


• 
  Thor: The Dark World (2013)
  
  
  
  
  • 
    Agents of SHIELD (Season 1) - The Well (ep. 8) to The End of the Beginning (ep. 16)
  
  
  
  


• 
  Captain America: The Winter Soldier (2014)
  
  
  
  
  • 
    Agents of SHIELD (Season 1) - Rest of season
  
  
  
  


• 
  Guardians of the Galaxy (2014)
  
  
  
  
  • 
    Agents of SHIELD (Season 2) - Up until The Dirty Half Dozen (ep. 19)
  
  
  
  


• 
  Avengers: Age of Ultron (2015)
  
  
  
  
  • 
    Agents of SHIELD (Season 2) - Rest of season
  
  
  
  


• 
  Ant-Man (2015)
  
  
  
  
  • 
    Agent Carter (Season 1)
  
  
  • 
    Daredevil (Season 1)
  
  
  • 
    Jessica Jones (Season 1)
  
  
  
  

Phase Three

• 
  
  • 
    Agents of SHIELD (Season 3) - Up until Failed Experiments (ep. 19)
  
  


• 
  Captain America: Civil War (2016)
  
  
  
  
  • 
    Agents of SHIELD (Season 3) - Rest of season
  
  
  • 
    Agent Carter (Season 2)
  
  
  • 
    Daredevil (Season 2)
  
  
  • 
    Luke Cage (Season 1)
  
  
  • 
    Agents of SHIELD (Season 4)
  
  
  
  


• 
  Doctor Strange (2016)
  
  
  
  
  • 
    Iron Fist (Season 1)
  
  
  
  


• 
  Guardians of the Galaxy Vol. 2 (2017)


• 
  Spider-Man: Homecoming (2017)
  
  
  
  
  • 
    The Defenders (Season 1) (2017)
  
  
  
  


• 
  Thor: Ragnarok (2017)
  
  
  
  
  • 
    Inhumans (Season 1)
  
  
  • 
    The Punisher (Season 1)
  
  
  • 
    Runaways (Season 1)
  
  
  • 
    Agents of SHIELD (Season 5)
  
  
  
  


• 
  Black Panther (2018)
  
  
  
  
  • 
    Jessica Jones (Season 2)
  
  
  
  


• 
  Avengers: Infinity War (2018)
  
  
  
  
  • 
    Cloak and Dagger (Season 1)
  
  
  
  


• 
  Ant-Man and The Wasp (2018)

Future film releases:

• 
  Captain Marvel (March 2019)


• 
  Avengers: Endgame (May 2019)


• 
  Spider-Man: Far From Home (July 2019)


• 
  Guardians of the Galaxy: Vol 3 (2020)


• 
  Black Panther 2 (20XX)


• 
  Black Widow (20XX)


• 
  Doctor Strange 2 (20XX)


• 
  Ms. Marvel (20XX)

(* The only exceptions are with the "One-Shot" short movies, which were only "released" on Bluray editions of the main movies. I've placed these directly after the movies they relate to for ease of viewing.)

1. Iron Man


2. Iron Man 2


3. Incredible Hulk (Hulk's campus rampage overlaps with Iron Man 2)


4. Thor (end of Iron Man 2 overlaps with the middle-ish of Thor; Jane Foster's science partner references the experiment that created the Hulk)


5. Captain America: The First Avenger (it can be assumed, from the post credits scene, that Nick Fury has already assembled the rest of the team; obviously if we are going in true chronological order, then you would watch the first 95% of this movie before Iron Man, and then the last bit after Thor)

Granted, watching them in this order or release date order won't change the experience I would say. But that is how they take place, chronologically.

EDIT To go even further, this site has a day-by-day breakdown of the events of the Marvel films.

I'd watch Iron Man before Iron Man 2, for the obvious reason. Other than that, watch them in whatever order you can get your hands on them. The references aren't particularly thick or important, they tend to rely more on general comic-book knowledge than the other films, and even if you don't know what they are you're unlikely to lose much enjoyment of the movie.

There’s a lot of answers already but I’m posting an answer anyway because most of the answers are lacking when it comes to Phase 3.

If you are looking for just the movies in the MCU,

1. Captain America : The First Avenger


2. Iron Man


3. Iron Man 2


4. The Incredible Hulk


5. Thor


6. Avengers


7. Iron Man 3


8. Thor : The Dark World


9. Captain America: The Winter Soldier


10. Guardians of the Galaxy


11. Guardians of the Galaxy Vol 2


12. Avengers: Age of Ultron


13. Ant-Man


14. Captain America: Civil War


15. Doctor Strange


16. Thor : Ragnarok


17. Spider-Man: Homecoming


18. Black Panther


19. Avengers : Infinity War

Here’s a much more in-depth look into the MCU,

PHASE 1

1. Captain America: The First Avenger


2. Agent Carter (season 1)


3. Agent Carter (season 2)


4. Agent Carter (one-shot on Iron Man 3 DVD)


5. Iron Man


6. Iron Man 2


7. The Incredible Hulk


8. The Consultant (one-shot on the Thor DVD)


9. A Funny Thing Happened on the Way to Thor's Hammer (one-shot on the Captain America: The First Avenger DVD)


10. Thor


11. Avengers


12. Item 47 (one-shot on the Avengers Assemble DVD)

PHASE 2

13. Iron Man 3


14. All Hail the King (one-shot on the Thor: The Dark World DVD)


15. Agents of SHIELD (season 1, eps 1-7)


16. Thor: The Dark World


17. Agents of SHIELD (season 1, eps 8-16)


18. Captain America: The Winter Soldier


19. Agents of SHIELD (season 1, eps 17-22)


20. Guardians of the Galaxy


21. Guardians of the Galaxy Vol 2


22. Daredevil (season 1)


23. Agents of SHIELD (season 2, eps 1-10)


24. Jessica Jones (season 1)


25. Agents of SHIELD (season 2, eps 11-19)
    26.Avengers: Age of Ultron
    


26. Agents of SHIELD (season 2, eps 20-22)


27. Daredevil (season 2, eps 1-4)


28. Luke Cage (season 1, eps 1-4)


29. Daredevil (season 2, eps 5-11)


30. Luke Cage (season 1, eps 5-8)


31. Daredevil (season 2, eps 12-13)


32. Luke Cage (season 1, eps 9-13)


33. Ant-Man


34. Agents of SHIELD (season 3, eps 1-10)

PHASE 3

36. Agents of SHIELD (season 3, eps 11-19)


37. Iron Fist (season 1)


38. 
    Captain America: Civil War
    39.Agents of SHIELD (season 3, eps 20-22)


39. The Defenders (season 1)


40. Agents of SHIELD (season 4, eps 1-6)


41. Doctor Strange


42. Thor: Ragnarok


43. Agents of SHIELD (season 4, eps 7-8)


44. Agents of SHIELD: Slingshot (season 1, eps 1-6)


45. Agents of SHIELD (season 4, eps 9-22)


46. Spider-Man: Homecoming


47. Black Panther


48. Inhumans (season 1)


49. The Punisher (season 1)


50. Runaways (season 1)


51. Agents of SHIELD (season 5, eps 1-10) – allowing for time travel craziness


52. Jessica Jones (season 2)


53. Agents of SHIELD (season 5, eps 11-19)


54. Avengers: Infinity War

While this isn't an official viewing order, some slight changes from the original release order can put crossover scenes/events closer to their eventual pay-off, without confusing the in-universe chronology any more than it already is.

Asterisks mark movies pulled forward from their original release order:

1. Iron Man


2. Iron Man 2 *


3. The Incredible Hulk


4. Thor


5. Captain America: The First Avenger


6. The Avengers


7. Thor: The Dark World *


8. Guardians of the Galaxy *


9. Iron Man 3


10. Captain America: The Winter Soldier


11. Avengers: Age of Ultron


12. Ant-Man


13. Captain America: Civil War


14. Spider-Man: Homecoming *


15. Black Panther *


16. Doctor Strange


17. Guardians of the Galaxy Vol. 2


18. Thor: Ragnarok


19. Avengers: Infinity War


20. Ant-Man and the Wasp

Defend!

Iron Man 2

As noted elsewhere, one of the last scenes in Iron Man 2 includes news footage from the university incident in The Incredible Hulk, suggesting that the climax of Hulk happens after Iron Man 2.

In addition, Iron Man 2 opens with Tony's press conference at the end of Iron Man playing live on TV.

Tony Stark's pre-credit appearance in Hulk works just as well if we assume he's visiting General Ross in his capacity as a consultant on the Avengers Initiative.

Thor 2 and Guardians 1

Thor: The Dark World begins (Dark Elves flashback excepted) with Loki being brought back to Asgard as a prisoner, allowing us to see the immediate fallout of The Avengers. Its mid-credits scene features the Collector, so it's nice to follow it with Guardians of the Galaxy to get immediate pay-off there, and to keep the space-based movies together.

Nothing in Thor 2 or Guardians spoils any of Iron Man 3 or Winter Soldier, which are both set on earth, and without spoiling anything, have some thematic parallels.

Spider-Man and Black Panther

Spider-Man: Homecoming and Black Panther can slot in immediately after Civil War, so that we get to know the two new characters introduced there immediately.

Nothing in either movie particularly affects the overall in-universe chronology, and we also get the benefit of:

• putting the Doctor Strange mid-credits sequence closer to its payoff in Thor: Ragnarok, and the movie as a whole closer to his appearance in Infinity War
  


• leaving the tonally-similar space-based Guardians 2 and Ragnarok right next to each other; and


• having the Ragnarok mid-credits sequence be followed immediately (well, after a short Goldblum comedy interlude) by its payoff in Avengers: Infinity War.

I know it's a bit late, but there is someone who made a fan edit of all five movies, joining them together to make a single, 9-hour movie called Avengers Assemble. It edited the films together in (roughly) chronological order.

Personally I'm going with this order:
Cap, IM1, IM2, Hulk, then Thor.

Part of Hulk is going on during IM2 (campus smash in on the screens while Fury is telling Stark he is only a consultant). Plus the end of Hulk has Stark saying they are putting together a team so IM2 ends before Hulk does. But Thor has begun before IM2 ends (Mjolnir after the credits). I feel its IM1, IM2, Hulk, Thor (end of Thor has Loki with the cosmic cube) but Cap is throwing me off. Yes Cap in in WWII so that should put it at the beginning of my viewing list, it is that last scene after the credits about "trying to save the world" that throws me off. IM1 ends with Fury admitting their are other super heroes out there and that the Avengers Initiative is already in place. So put Cap at the front of my list; Cap, IM1, IM2, Hulk, Thor, Avengers. The ending of Cpt America is actually a scene from the avengers

Here's the list I would go with:

Captain America: Just the fact that it does happen before everything. Even though it makes references to the other movies it makes the other ones much better to watch.

Iron Man: At the end you hear Nick talk about other heroes, and he can be referring to Cap.

Iron Man 2: You do see or hear references about Thor, like Agent Coulson has to leave to go check out something in the desert. And Hulk with the whole campus thing in the background.

Thor: For this is pretty tricky, the first 3 are a lock. It just depends on what viewpoint you want to go with, between Thor and the Hulk. During IM2, when Coulson leaves, it's way before the Campus thing. So Thor has a little edge over that one. If you want to go with the end scene to Thor and the Cosmic Cube, well they find it during Captain America. And at the end of IM2, you see the Hammer which everyone knows.

Hulk: He's such a badass you have to have him last. The super soldier serum didn't create the Hulk (more like the start of Abomination), as someone said above, but still a great reference to CA. Tony comes at the end to recruit, even though he's not on the team yet, but he's a consultant. I read somewhere a while ago that when the campus fight happens, a mysterious fog comes through, that's suppose to be Thor's doing.

So Capt. America, IM, IM2, Thor, Hulk = Avengers (in my opinion).

The order is

1. Captain America


2. The Hulk


3. Iron Man


4. The incredible Hulk


5. Iron Man 2


6. Thor


7. Avengers


8. Iron Man 3


9. Thor 2


10. Captain America: the winter soldier

They are all stuffed up. The ends of all the movies don't match. But here is my info, and they are in order of how I might watch them before seeing the avengers movie :)

In Captain America, like, 90 or 95% is a flash back. The start and end are in 'our times' and in the end, in 'our time', he wakes up, and gets spoken to and stuff by Nick. Also - Captain America gets Howard Stark (Tony's - Iron Man's - dad,) to make the shield.

Iron Man 1, that's all good, at the end Nick talks to him, a bit.

But in Hulk there is some talk about the super solder serum (stuff that was used on Captain America) was the stuff used on Hulk. But it was clearly altered. At the end of the movie, Tony comes in and talks about this 'group' (Avengers) but if you were to watch it in the order I have it, it would be wrong-ish... because Tony doesn't get asked/told about the avengers group until the end of the second Iron Man..

In Iron Man 2 Tony sees more of Nick and at the end, Nick tells him about the Avengers, (S.H.I.E.L.D.), but when Nick is talking to Tony at the very end, if you look at the screens behind, you see the Hulk, bashing up stuff, the same stuff (same clip from the Hulk movie) and at the very very very end, the guys at S.H.I.E.L.D. find Thor's hammer.

In Thor you see alot of S.H.I.E.L.D, and at one point, you see HawkEye. (appears again in the Avengers movie) so this movie should be at the end of you list, because they talk about Steve (Capt. America)'s disappearance... (sleeping for like 70 years..) and when the 'destroyer' comes, one guy says he thinks it's Iron Man.