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There is always something beneath the surface.

Behind it all, behind [[Franchise/SpiderMan the amazing]], [[ComicBook/IncredibleHulk the incredible]], [[ComicBook/FantasticFour the fantastic]] and even [[ComicBook/XMen the uncanny]], there exists dangers and threats that are rarely seen because they hide in the shadows or are too massive for most of the world to comprehend. Yet there is one organization that has taken it upon itself to safeguard the human race against the known and unknown. They are security, they are shelter... they are the S.H.I.E.L.D..

S.H.I.E.L.D. is the source of most, if not all, of the SpyFiction in the Franchise/MarvelUniverse. It is the nebulous espionage organization that for decades was known as the "House that ComicBook/NickFury built". It first appeared in ''Strange Tales'' #135 (August, 1965). The organization is a UN or sometimes United States backed paramilitary and intelligence organization, whose acronym originally stood for Supreme Headquarters, International Espionage, Law-Enforcement Division but was changed in the [[TheNineties 1990s]] to stand for Strategic Hazard Intervention, Espionage and Logistics Directorate. In the Franchise/MarvelCinematicUniverse, the acronym was defined as the "Strategic Homeland Intervention, Enforcement, and Logistics Division".

There have been numerous series revolving around and featuring S.H.I.E.L.D. throughout the years, including long standing features in multiple ''ComicBook/CaptainAmerica'' runs. In the 2010s, Creator/JonathanHickman began delving deeper into the organization's history; first in ''ComicBook/SecretWarriors'' and then in [[ComicBook/SHIELD2010 two bimonthly mini-series]]. [[ComicBook/SHIELD2014 Another series]] launched in December 2014, essentially being an in-universe version of the first season of the ''Series/AgentsOfSHIELD'' TV show with Agent Coulson leading a team to investigate whatever weird stuff S.H.I.E.L.D. needs investigating; this was later relaunched under the show's title of ''ComicBook/AgentsOfSHIELD''.

For some of S.H.I.E.L.D.'s most prominent agents, see ComicBook/NickFury, Sharon Carter (codename "ComicBook/{{Agent 13}}"), ComicBook/MariaHill, and ComicBook/DaisyJohnson (codename "Quake").

S.H.I.E.L.D. has also been a large part of several Marvel adaptations, including ''WesternAnimation/SpiderManTheAnimatedSeries'', ''WesternAnimation/TheAvengersEarthsMightiestHeroes'' and ''WesternAnimation/UltimateSpiderMan''. S.H.I.E.L.D. features notably in the Franchise/MarvelCinematicUniverse as an important part of the series, being a recurring element in several movies and the focus of two TV spinoffs, ''Series/AgentsOfSHIELD'' and ''Series/AgentCarter''.

!!The S.H.I.E.L.D. organization provides examples of:

* AppliedPhlebotinum
* BadassNormal: Most agents don't have superpowers but that doesn't stop them from being a force to be reckoned with in a world filled with mutants, gods, aliens, and super soldiers.
* BeethovenWasAnAlienSpy: Creator/JonathanHickman's ancient version of SHIELD is constructed '''entirely''' from this trope.
* BreakingTheFellowship: Particularly in modern series, S.H.I.E.L.D. has a habit of getting dissolved whenever they screw up so badly or are corrupted too much to be effective. The first time had Fury dismantle the original gathering when a group of LMDs gained sentience and took over. The second time was caused by the fallout of ''ComicBook/SecretInvasion'' and the third due to the fallout of ''ComicBook/SecretEmpire''.
* CanonImmigrant: Agent Phil Coulson from the Franchise/MarvelCinematicUniverse.
** And, depending on your definition, Creator/SamuelLJackson lookalike Nick Fury Jr.
** Many members of the ''Series/AgentsOfSHIELD'' cast made their way to the comics in the 2014 series.
* CloakAndDagger
* DependingOnTheWriter: Their sense of integrity and competence can highly vary between the stories they are in (both comics and adaptations) as they can be a highly effective team against the forces of evil or a LawfulStupid force that is more of a hindrance to other heroes than help. Sometimes, it simply depends on which agent you're dealing with.
* ElaborateUndergroundBase: They love these. In the earlier comics it was accessible through a special chair in a certain barbershop that would descend into the floor. Nowadays they tend to have a less dramatic base.
* FunWithAcronyms: One of the most notorious examples of it. This extends to related organizations S.T.R.I.K.E.[[note]]Special Tactical Reserve for International Key Emergencies[[/note]], S.W.O.R.D.[[note]]Sentient Worlds Observation and Response Department[[/note]], and A.R.M.O.R.[[note]]Alternate Reality Monitoring and Operational Response[[/note]]. Parodied with H.A.M.M.E.R., which never had its meaning defined and characters in-universe made jokes that nobody knew what it stood for.
** How about S.H.I.E.L.D. itself, which has gone through a few variatons?
*** ''Supreme Headquarters, International Espionage, Law-enforcement Division'' from when it first appeared in 1965 through the end of TheEighties.
*** ''Strategic Hazard Intervention Espionage Logistics Directorate'' starting in 1991 when the organization was rebooted following the events of ''Nick Fury vs. S.H.I.E.L.D.''.
*** ''Strategic Homeland Intervention, Enforcement and Logistics Division'' in modern adaptations, including the Franchise/MarvelCinematicUniverse. (The word "Homeland" having become in vogue since the creation of the Department of Homeland Security after 9/11.)
--->'''Maria Hill:''' What does S.H.I.E.L.D. stand for?
--->'''Agent Ward:''' Strategic Homeland Intervention Enforcement and Logistics Division
--->'''Maria Hill:''' What does that mean to you?
--->'''Agent Ward:''' It means someone really wanted our initials to spell S.H.I.E.L.D.
** Creator/JackKirby's original artwork had Nick Fury as "The Man Called D.E.A.T.H."[[note]]Director of External Atomic Threat Headquarters[[/note]]. When the artwork was eventually used for the 50th anniversary, The Man Called D.E.A.T.H. was instead the mysterious figure who recruited S.H.I.E.L.D. directors.[[note]][=DaVinci=] Elevating Agents To Helm[[/note]]
* GoodIsNotNice: They often like to go by this motto even in their more favorable depictions. Though of course whether the "Good" part has any credibility is DependingOnTheWriter.
** For example, references are made in the MCU to SHIELD conducting assassinations, it hires characters such as Comicbook/BlackWidow and Comicbook/{{Hawkeye}} who are described directly as being killers, and has on occasion sanctioned the murder of civilians such as in the ''Film/Item47''. All for the greater good, so they say. That said, however, given the revelations in ''Series/AgentsOfSHIELD'' and ''Film/CaptainAmericaTheWinterSoldier'' that [[spoiler:many SHIELD operatives are in fact working for HYDRA]], the extent to which the trope actually applies in this continuity is uncertain.
* GadgeteerGenius: In the 60s SHIELD actually had an armorer named [[Franchise/JamesBond Boothroyd]]. Later on they got the Sidney "The Gaffe" Levine, who was retconned into being a former member of the WWII team Sky-Wolves. Somehow neither has appeared recently.
* GovernmentAgencyOfFiction
* HubcapHovercraft: Their hovercars are often depicted as working this way.
* JerkAss: This appears to actually be a requirement if you want a job with this group. Averted in the movies, though, especially by Agent Coulson (who ''can'' be a jerk when he wants to be; he's just [[AffablyEvil polite about it]]).
* {{MacGuffin}}: Has had many of them, one of the latest being the Human Machine in the new series
* TheOmniscientCouncilOfVagueness: S.H.I.E.L.D. usually has one of these in the background pulling their strings, even when Nick Fury was in charge.
* OverlyLongName: The organization's full name in the comics has varied, but the movies present it as the Strategic Homeland Intervention, Enforcement, and Logistics Division. ''Film/IronMan1'' used it as a RunningGag and, until the acronym was officially revealed at the end, a StealthPun.
* RedshirtArmy: Despite the fact that they are sometimes shown as MenOfSherwood or even BadassArmy, S.H.I.E.L.D. agent usually serve just as victims to be easily killed by any villain. Any commander will not usually really care about the losses. It sometimes seems that they do not even care about casualties when they plan their actions. Many agents or soldiers are killed in large numbers for example on board of the Hellicarriers that seem to serve mostly just so they can fall down and kill all their crew. How S.H.I.E.L.D. HR department manages to recruit anyone is a mystery.
* {{Retcon}}: Technically, S.H.I.E.L.D. itself started with a retcon reviving [=WW2=] hero Nick Fury to be both their top agent and partial creator. ''ComicBook/SecretWarriors'' and the 2010 series dived into the organization's history, adding a lot more (see below).
* RidiculouslyHumanRobots: Life Model Decoys
* StateSec: A good guy version of one: A spy [=/=] law enforcement agency with a AirborneAircraftCarrier and other quasi-military elements.
* SpyCatsuit
* SpyVersusSpy
* TooDumbToLive: They have had their moments, especially in ''VideoGame/SpiderManShatteredDimensions'' when they tried to use Carnage and give it a lot more power and it worked as well as one would think it would.
* UnitedNationsIsASuperpower: Inconsistent between this and being a United States force.