Marvel Phase 1 Guide: The Avengers
Viewing Order Placement
This one’s simple. Every other movie in Phase 1 builds towards The Avengers in ways both big and small, and this movie lays the groundwork for everything still to come in Phase 2 and beyond.
Additionally, Banner reveals he hasn't turned into the Hulk in more than a year, and Fury notes that the events of Thor happened "last year," placing this movie at least a year later than Iron Man 2, The Incredible Hulk, and Thor.
easter eggs and references
LMD: Tony Stark jokes to Coulson that he's actually a Life Model Decoy. More commonly referred to as LMDs, this type of synthetic being will become a problem for S.H.I.E.L.D. years later.
The Cellist: Coulson mentions he is dating a Cellist, a character who will eventually appear in an episode of Agents of S.H.I.E.L.D.
Homework: When Stark opens the files on The Avengers, footage from previous films can briefly be seen on display.
Odin’s Eyes: In Norse mythology and the MCU, Odin is known for having two all-seeing ravens that serve as his eyes and ears away from Asgard's throne. These ravens can be seen when Thor first appears to speak with Loki.
Phase Two: Steve Rogers discovers that S.H.I.E.L.D. has been experimenting with Hydra weapons, foreshadowing the events to come in Captain America: The Winter Soldier.
New Nickname: Tony notes that the Avengers are "Earth's Mightiest Heroes," a label they are commonly given in the comics.
The Man Behind the Curtain: The first post-credits scene reveals that the events of the movie were orchestrated by the alien Thanos who will go on to serve as the primary antagonist of the Avengers and Guardians of the Galaxy for years to come.