Over the near six-decade journey of “Star Trek,” audiences have witnessed numerous Starfleet officers who choose to defy these regulations. Often, these are characters like the rebellious Ro Laren (Michelle Forbes) or the rule-averse Tom Paris (Robert Duncan McNeill), who find themselves reluctantly integrated into starship crews. Surprisingly, even some of the most disciplined officers have occasionally bent the rules, challenging Starfleet directives. So, prepare to be briefed on five “Star Trek” episodes where characters boldly go against the grain.

In “Star Trek,” the regulations guiding Starfleet draw heavily from modern military practices, which includes Regulation 1138. This rule explicitly bans romantic relationships between officers within the same command hierarchy. Although often overlooked for the sake of a compelling romance, the most notorious breach occurs in “Deep Space Nine,” when Commander Worf (Michael Dorn) and Lt. Dax (Terry Farrell) become romantically involved, culminating in the episode “Looking for Par’Mach in All the Wrong Places.”

In the fifth season episode “Change of Heart,” Worf is at the helm of the Defiant on a vital mission during the Dominion War. But when Dax’s life is endangered, he opts to abandon the mission to rescue her, a choice that carries significant consequences. Sisko warns Worf that his actions likely cost him any future opportunities to command a starship.

The prequel series “Star Trek: Enterprise” reveals Earth’s initial contact with the Romulan Empire in the 22nd century, which eventually leads to an interstellar conflict spanning centuries. By the early 24th century, however, an uneasy peace is established with the signing of the Treaty of Algernon. This treaty, as later disclosed, includes a clause forbidding the Federation and Starfleet from developing cloaking technology, a restriction stemming from their resolution with the Romulans.

In that Season 5 episode, Worf takes command of the Defiant on a crucial mission with enormous stakes in the war with the Dominion. But when Dax’s life is on the line, Worf chooses to abandon the mission to save his par’Mach. It’s a decision that costs him, as Sisko tells Worf he’ll likely never be given the captain’s chair again.

As seen in the prequel series “Star Trek: Enterprise,” Earth’s first contact with the Romulan Empire occurs in the 22nd century, and the two powers would eventually duke it out in an interstellar war, leading to hundreds of years of conflict. In the early portion of the 24th century, however, the Romulans and the Federation signed a precarious peace accord, the Treaty of Algernon. Part of that treaty, we’d later learn, was an agreement by the Federation and Starfleet to never develop any form of cloaking technology.

In the “Star Trek: The Next Generation” episode “The Pegasus,” however, we learn that Starfleet didn’t exactly abide by this agreement. In secret, they developed a new kind of cloaking device that was even more powerful than the one the Romulans employed. In addition to turning a ship invisible, it could also turn a vessel intangible, allowing it to pass through solid matter. It was a top-secret project spearheaded by Captain Eric Pressman (Terry O’Quinn), but the first experimental ship was thought lost. When it turned up, more than a decade later during the events of “The Pegasus,” it created problems for Commander Riker (Jonathan Frakes), who’d served under Pressman and was ordered not to divulge their breach of the peace treaty.

Ultimately, the Romulans did learn about the existence of Starfleet’s phasing cloak, and Captain Picard fessed up to them at the tail end of the episode. Sadly, however, the phasing cloak wound up as a plotline that never truly paid off.

The crew aboard “Deep Space Nine” was full of rule breakers; the series’ antiheroes and morally grey protagonists are part of what made it so compelling, after all. But it wasn’t just characters like the former Cardassian spy Garak, one-time terrorist Major Kira, or Klingon warrior Worf who broke the rules. In fact, the ship’s commanding officer, Captain Benjamin Sisko (Avery Brooks), often seemed just as willing to cast aside the rulebook. Though his most famous moral transgression comes in the episode “In the Pale Moonlight,” he does so again, with more direct consequences, in “For the Uniform,” in one of many “Star Trek” moments that went too far.

“For the Uniform” sees the return of Michael Eddington (Ken Marshall), who was revealed to be an undercover Maquis agent in the episode “For the Cause.” Now, he’s back, and Sisko is hot on his tail and seemingly obsessed with putting him behind bars for his treachery. It’s an obsession that Eddington himself likens to that of Jean Valjean in “Les Misérables,” and of course, Eddington sees Sisko as the villain. He may be more right than you’d expect, because at the climax of the episode, after Eddington uses a biological weapon to poison the atmosphere of a Cardassian planet, Sisko retaliates by doing the same, firing a poison torpedo that decimates the atmosphere of a planet the Maquis call home. It’s a decision that’s questioned even within the episode as something Starfleet’s rules of engagement would never allow.

When one thinks of away teams in “Star Trek,” they typically imagine a group of mostly anonymous red shirts who get mowed down at the first sign of trouble while the show’s stars escape. But there’s a good reason why it’s usually nameless crewmen who bite the phaser beam. A longstanding Starfleet rule prohibits a ship’s captain and first officer from both serving on an away team. And it certainly makes sense: If they encounter trouble, you wouldn’t want the ship to be without its captain and their backup. The “Star Trek: The Next Generation” episode “Time’s Arrow,” however, sees Captain Picard flagrantly ignoring this rule, and for a deeply personal reason.

The episode begins with the discovery of Data’s head deep beneath the surface of San Francisco, making it clear that at some point, he will travel into the past and die there. But the enigmatic bartender Guinan (Whoopi Goldberg) knows what’s about to happen because she was there the first time around, living on Earth in the late 19th century. When Data is indeed lost after stepping through a portal into the past, Guinan tells Picard that, despite regulations, it’s critical that he and Riker be on the away team that follows the android.

As Guinan knows, these events have already happened because she lived through them. She was there when Picard came to her aid in the 19th century, and she alone knows how important it is that he follow through with history as she remembers it — regulations be damned.

Because time travel seems to be relatively common in the world of “Star Trek,” the Temporal Prime Directive establishes the parameters for such jaunts into the past or future. These rules include, among other things, not divulging your status as a time traveler and never cluing in the natives about what the future holds.

When characters in “Star Trek” break the Temporal Prime Directive, however, it’s usually for a justifiable reason with a greater good in mind, or, as in the case of the “Deep Space Nine” episode “Trials and Tribble-ations,” to get an innocent autograph. But in the “Star Trek: Voyager” series finale “Endgame,” a future Admiral Janeway goes back in time to change the past, not for some grand, greater good, but for her own personal desires, hoping to get her crew home sooner and ensure that several friends who’d died along the way are never killed.

Not only that, but when Admiral Janeway goes back in time and visits her younger self, who is still in the Delta Quadrant, she doesn’t just try to change the past. She openly recruits her past self and tells the crew of Voyager all about what happens to them between their present and hers. It’s such a gross violation of the Temporal Prime Directive that even the younger, present Janeway objects. However, she does ultimately go along with the plan — which, of course, succeeds and erases decades of history in the process.