The Infinity Stones are items with reality-altering powers that exceed every other force or power shown so far in the Marvel Cinematic Universe. When all of them are collected in an Infinity Gauntlet, the wielder is given power to destroy complete universes. Up to this point, two Infinity Gauntlets have been revealed, a right-handed one was briefly shown in Thor inside Odin's chambers, and a left-handed is worn by Thanos (as revealed in this movie's mid credits scene). It's hinted that only extraordinary individuals can survive touching the stones barehanded, and even in that case, it requires great willpower to use the power of the Stones without a Gauntlet itself. In a proper film making point of view, these items are the driving force that keeps the entire Marvel Cinematic Universe franchise united. At the end of "Age of Ultron", four of the six Stones have been revealed and located:
- Blue (Space Gem): Hidden inside the Tesseract, it can open portals to between universes. First seen in Captain America: The First Avenger, where the Red Skull located it in a Norwegian monastery and used its energy to create highly advance weaponry during WWII. It's hinted in Iron Man 2 that the original Arc Reactor technology used by Iron Man was designed based on knowledge Howard Stark once he recovered the Tesseract. In The Avengers, Loki and a mind-controlled Erik Selvig use it to open a portal to let the Chitauri army enter the Earth. Also, it's revealed that S.H.I.E.L.D designed new weaponry based on confiscated, Tesseract-powered HYDRA technology as a backup in case the Avengers Initiative would fail. After Loki's defeat, Thor took it back to Asgard. It's kept in Odin's chambers and accessible to Loki once again, as well as the aforementioned Infinity Gauntlet, having taken control of Asgard during the events of Thor: The Dark World.
- Red (Reality Gem): Hidden inside the Aether, it has the ability to transform matter into dark matter. First seen in Thor: The Dark World, thousands of years ago in a war where King Bor of Asgard (father of Odin) defeated Malekith, leader of the dark elves. In modern times, Dr. Jane Foster discovered it once again while studying gravitational disturbances in London, putting her own life in danger. During the events of the Convergence, Malekith briefly took control of it inside his body, rendering him nearly invincible. After Thor's victory over him, it was handed over to The Collector to avoid having two Infinity Stones together in the same place. The Collector's alliances and ultimate goal are unknown at this point, but he is shown saying "one down, five to go..."
- Yellow (Mind Gem): Hidden inside Loki's scepter, it has the ability to control minds as well as create new ones, such as Ultron and The Vision. First seen in The Avengers when it is assumed that Thanos himself and/or The Other (leader of the Chitauri army) gave it to Loki. With it, Loki stabbed and killed Agent Phil Coulson, causing Iron Man, Black Widow, Thor, Captain America, Hawkeye and Hulk unite to avenge him. Natasha Romanoff (Black Widow) used it to close the portal Loki and a mind-controlled Dr. Selvig created to let the Chitauri army attack New York. S.H.I.E.L.D. took it into custody for study. In the aftermath of S.H.I.E.L.D.'s demise in Captain America: The Winter Soldier, HYDRA leader Baron von Strucker took control of it and used it for power-inducing human experimentation, including the Maximoff twins, giving birth to what he called "the age of miracles". After recovering the scepter, Tony Stark and Bruce Banner integrate the data collected from Loki's Scepter into the Ultron Program, inadvertently creating a new foe who wants to use this Gem and a vibranium-based body to make himself invincible and destroy all human life. However, additional data inside the Gem itself, the mentioned body and part of JARVIS artificial intelligence created the benign entity called The Vision, who currently controls the Gem.
- Purple (Power Gem): Hidden inside The Orb. First seen in Guardians of the Galaxy, it has the ability to destroy entire planets at a molecular level. In a distant, unknown past, an old being called a Celestial (one of whose decapitated skulls serves as a mining operation and part of a menagerie for the Collector, called 'Knowhere') is depicted using it to eradicate life in a planet with a single blow. At some point in the remote past, it was stored on abandoned planet Morag and lost in time until Peter Quill (aka Starlord) seized it from the planet's ruins just minutes before Kree soldiers under the command of Ronan the Accuser arrive to retrieve it. Ronan had the intention of wiping out the Xandarian civilization as revenge against them for an ancient war. Having each their own separate agendas, Ravager leader Yondu Udonta and The Collector (who at this point already has the Reality Gem), want to take control of it. Both Ronan and Star-Lord are seen surviving while using it barehanded for a short time. Following the failed massacre by Ronan, the Nova Corps, a planetary law enforcing organization based on Xandar, are seen protecting it. At the end of Age of Ultron, these events are hinted by Thor to his fellow Avengers just before returning to Asgard.
- Orange (Time Gem): Yet to be revealed.
- Green (Soul Gem): Yet to be revealed.
This last two Stones and their respective powers are to be revealed over the course of Phase 3 of the MCU (Captain America: Civil War, Doctor Strange, Guardians of the Galaxy Vol. 2, Thor: Ragnarök, Black Panther, Captain Marvel, Inhumans, Spider-Man: Homecoming), ultimately culminating in Avengers: Infinity War and Untitled Avengers Movie. Doctor Strange will reportedly expand on the mythology surrounding the Infinity Gauntlet and will most likely reveal the Orange Gem. Thor revealed that he will return to Asgard to learn more about the Infinity Stones, which will elaborate on the backstory of the Infinity Stones and their creation, presumably fully unveiled by Thor: Ragnarök. It is also highly rumored that Thor: Ragnarok will be the definitive setup for Infinity War.