When Nick Fury first realized that the universe is filled with powerful and dangerous threats in Captain Marvel, he made plans for an Avengers Initiative which would gather together some of Earth's most formidable protectors in case a new threat ever emerged. Thankfully he made that idea a reality decades later in Avengers, because without the S.H.I.E.L.D. director's leadership and the combined efforts of Iron Man, Captain America and the others, Loki and his Chitauri army likely would have taken over the planet.
The Avengers then went on to take down Ultron, Thanos and various other threats, but not without facing their share of internal problems along the way. The events of Captain America: Civil War proved just what chaos can happen if superheroes clash over rules and ideologies. That's why Nick Fury set these rules in place, to keep his team of Earth's Mightiest Heroes running smoothly and help them be the heroes Earth—and sometimes even the entire galaxy—needs them to be.
18 TEAM UP WITH COMPLETE STRANGERS
When Loki and his army invaded New York City, it didn't matter that the Avengers had never really fought as a team before—they had to adapt and learn to work together. Nick Fury has since made it a requirement for the Avengers to be willing to team up with complete strangers. The fate of the entire world is often on their shoulders, so Earth's Mightiest must remain flexible and learn how to fight alongside whoever volunteers to assist them.
Without this level of unity, the heroes of Endgame—most of whom didn't even know each other's names—never would have been able to defeat Thanos and his forces.
17 TRAIN WITH A VARIETY OF WEAPONS
Almost every member of the Avengers has some sort of signature weapon that they prefer to use. Cap has his iconic vibranium shield, Hawkeye has his bow and arrows, and Spider-Man has his web shooters. But Fury makes sure that they're able to fight using a variety of different weapons as well, just in case.
Clint and Natasha's mastery of various weapons gives them an advantage against nearly every adversary they face, even though they don't have superhuman powers. And Cap's work with Thor helped him wield Mjolnir flawlessly when he was deemed worthy in the Endgame fight against Thanos.
16 AVENGERS MUST PUT THE MISSION BEFORE THEIR PERSONAL LIVES
When the "Elementals" threatened to take over the world in Spider-Man: Far From Home, Nick Fury (or, technically, his proxy) expected Peter Parker to prioritize defeating them over having fun on his class trip. It seemed unfair to expect so much of a teenager, but that's the price of being an Avenger.
The members of Earth's Mightiest Heroes all have to put the mission above their personal lives. Luckily, several Avengers have figured out a way to balance their heroics with their romantic pursuits.
15 VENTURE INTO SPACE WHEN THE MISSION REQUIRES
Just because they're known as "Earth's" Mightiest doesn't mean the Avengers get to just stay on their own planet all the time. When a villain threatens to destroy or conquer the entire universe, Nick Fury expects everyone on the Avengers' roster to journey into space to fight against them.
In the end credits of Far From Home, viewers saw that this rule even applies to Fury himself. Talos the shape-shifting Skrull pretended to be him over the course of the film, so Fury could partake in a space mission of his own.
14 DON'T DEPEND ON FURY FOR RECRUITMENT
Nick Fury helped unite the original six members of the Avengers — Iron Man, Captain America, Hulk, Black Widow, Hawkeye, and Thor. But there's no way those six could have taken down Ultron or Thanos without help, so everyone was expected to play a part in recruiting other heroes.
Tony Stark helped bring War Machine and Spider-Man onto the team, and Cap recruited Sam Wilson, who went on to recruit Ant-Man. Thor brought in the Guardians of the Galaxy. If a single recruit wasn't on hand in Endgame's final battle against Thanos, the Mad Titan might have won again.
13 STAY READY FOR BATTLE AT ALL TIMES
Black Widow was one of the world's greatest spies and Captain America was likely Earth's best combatant, but they still constantly trained to hone their skills and become better superheroes.
During their limited off-time, Fury expects Earth's Mightiest to continue perfecting their special abilities, learning different fighting techniques, and staying in peak shape so they'll be ready if and when a new threat emerges.
12 FIGHT SUPERVILLAINS, NOT EACH OTHER
Nick Fury knows that the Avengers can only defeat their enemies if they work together as one cohesive unit, so he expects the Avengers to settle any internal disputes in a civilized manner and save the fighting for the bad guys.
Unfortunately, the Avengers can't help breaking this rule. Captain America and Iron Man nearly eliminated each other in Civil War, and their feud forced several other Avengers to square off as well. Thor and Hulk have clashed on numerous occasions. And then, of course, there were all those fights that happened when an Avenger was being mind-controlled.
11 DON'T BE EGOTISTICAL
Nick Fury has a bit of an ego himself, but he still expects his Avengers to keep their egos in check. In fact, he almost prohibited Tony Stark from joining the team because of his narcissistic tendencies.
It's always amusing to see the Avengers argue about who is the smartest or strongest, but these quarrels are definitely problematic because heroes shouldn't waste time on internal power struggles. Fury constantly reminds them that everyone on the team is there for a reason, and that they should all respect and value each other's contributions.
10 FIGHT MINOR VILLAINS SOLO
When Nick Fury told Spider-Man about the Elementals, Peter asked why he couldn't just round up the rest of the Avengers to help. Unfortunately, it's not quite so easy to get Earth's Mightiest together, so members are expected to take down minor threats all by themselves.
Thor and Captain Marvel are often off-planet, Hawkeye tries to live a normal life with his secret family, and Black Panther has a kingdom to run. Unless the entire planet is in danger, heroes have to be willing to at least try fighting solo.
9 DEVELOP HEROIC CODE-NAMES
Not every superhero needs to have a secret identity, but every member of the Avengers is expected to come up with a cool superhero name. No villain would be afraid of powerless individuals who solely refer to themselves as Clint and Natasha, but "Hawkeye" and "Black Widow" sound far more formidable and intimidating.
Doctor Strange is one of the few exceptions to this rule, but that's just because the Sorcerer Supreme's name sounds heroic as it is.
8 KEEP S.H.I.E.L.D. SECRETS
When HYDRA made an attempt on Nick Fury's life in Captain America: The Winter Soldier, Cap and Black Widow were expected to keep the secret about his survival to themselves. The Avengers occasionally question Fury's morals and motives, but they can't go around telling people about their concerns.
What happens in S.H.I.E.L.D. stays in S.H.I.E.L.D., especially since deep cover HYDRA spies are everywhere and even the government can't be trusted with the organization's intel and weapons.
7 RECOVER DANGEROUS AND POWERFUL ARTIFACTS
The Marvel Cinematic Universe is absolutely filled with dangerous artifacts which could cause a lot of chaos and destruction if they wound up in the wrong hands. Vulture used Chitauri tech to commit crimes in Homecoming, HYDRA used Loki's staff from Avengers to create Scarlet Witch and Quicksilver, and Red Skull used the Tesseract to power up HYDRA's weapons.
The Avengers are expected to round these powerful items up, so S.H.I.E.L.D. and Nick Fury can ensure they are disposed of or kept hidden from the world.
6 FOLLOW THE CHAIN OF COMMAND
Even though Nick Fury was the one to initially bring the Avengers together, he isn't necessarily the team's leader. Captain America typically calls the shots when they're in battle together, and Earth's Mightiest Heroes are expected to follow his orders.
When an Avenger leader is unavailable, members have to follow the chain of command and take direction from the next hero in line.
5 WORK WITH THE GOVERNMENT
Nick Fury may not have initially planned for the Avengers to work directly with the government, but after the events of Civil War caused world leaders to decide that Earth's Mightiest Heroes could no longer be trusted to operate independently, his hand was forced.
The Avengers were expected to obey orders from the UN and Secretary of State Thaddeus "Thunderbolt" Ross. Fury never technically provided his input on this development, but since he was once head of a government organization, we can assume he wants his team to follow the law whenever possible.
4 TAKE DOWN S.H.I.E.L.D.'S VILLAINOUS RIVAL, HYDRA
Peggy Carter helped found S.H.I.E.L.D. as a response to HYDRA after the events of Captain America: The First Avenger, and ever since then, the two organizations have been rivals.
The agents of S.H.I.E.L.D. can typically hold their own against HYDRA, but every now and then, the Avengers are expected to step in and provide some assistance. Cap, Falcon and Black Widow helped thwart HYDRA's plan for world domination in Winter Soldier, and all of Earth's Mightiest teamed up to reclaim Loki's staff from them in Age of Ultron.
3 START EACH BATTLE WITH A MOTIVATIONAL SPEECH
Nick Fury is a master of manipulation, and when Loki ended Phil Coulson's life in Avengers, he used the beloved agent's passing as a tool to finally motivate the Avengers to unite against their common enemy. His speech about forming a team of "remarkable people" to see if they could become something more was exactly what the heroes needed to put aside their differences and fight together, and became the first of many pre-battle motivational speeches in the Avengers' history.
2 BE PREPARED TO GO UNDERCOVER
Not everyone on the Avengers received spy training like Black Widow and Hawkeye did, but they're all expected to be able to investigate potential threats independently and go undercover when need be.
Natasha perfectly infiltrated Stark Industries to keep an eye on Tony Stark in Iron Man 2, Steve had to hide from the whole country when he was believed to be an enemy of the state in Winter Soldier, Scott Lang snuck into Pym Technologies to foil Yellowjacket's plans to sell Pym particles in Ant-Man, and Peter did his share of investigative work in Spider-Man: Homecoming.
1 PROTECT THE EARTH AT ALL COSTS
This is the most obvious rule Nick Fury expects the Avengers to follow, but it's also the most important. Earth's Mightiest Heroes have to protect the planet at all costs, even if that cost is their own lives or the lives of their loved ones.
When Natasha realized she had to sacrifice herself so Clint could get the Soul Stone the Avengers needed, she did so without hesitation. Tony Stark similarly knew that wielding the Infinity Gauntlet would result in his death, but he put the needs of the universe over his desire to continue living with his wife and daughter.