12 Rules Gibbs Swore By on NCIS and the Meanings Behind Them

Leroy Jethro Gibbs (Mark Harmon) lived by his rules on NCIS.

For 19 seasons, Gibbs spouted his guidance to his team of special agents, giving them a handbook to live and work by. The lead character had 91 rules, which have not all yet been revealed.

Actor Harmon left the series in 2021, but his character’s list of advice lives on with the prequel series NCIS: Origins, and the NCIS flagship, whose 22nd season concludes on May 5.

“My wife believed we all should have a code to live by, a set of rules,” Gibbs said in a voiceover, on the third episode of NCIS: Origins, the series following Gibbs’ early days with the Naval Criminal Investigative Service.

“And I believed in her. So for years, I wrote my own rules down on napkins, scraps of paper,” he continued. “I followed all of them to the letter.”

While the NCIS franchise continues to share more of the guidelines, here are 12 rules Gibbs swore by, and the meanings behind his words of wisdom.

No. 1: Never screw over your partner

The NCIS team must depend on one another, so trust and loyalty are essential to their work.

“Never screw over your partner” is Gibbs’ first rule, but according to Special Agent Timothy McGee (Sean Murray) in season 8, there is also another no. 1: “Never let suspects stay together.”

Whether it was Gibbs and Senior Field Agent Anthony DiNozzo (Michael Weatherly) out on the field or Dr. Donald “Ducky” Mallard (David McCallum) and Dr. Jimmy Palmer (Brian Dietzen) working hand-in-hand in the lab, partners leaned on each other.

No. 2: Always wear gloves at a crime scene

Wearing gloves at a gruesome crime scene is taken literally by the members of NCIS.

The rule can also be applied to being prepared to do your job, whether it’s a crime scene or not.

No. 3: Never believe what you are told; double-check

Gibbs taught his team to always have a healthy level of skepticism when it comes to investigations. He pushed the agents to confirm and verify the information they were given was correct, even if it came from a trusted source.

Like the first rule, the third rule has two entries, one of which is “Never be unreachable.” Although the agents split their time between the office and the streets, they need to maintain communication, including during their off hours, in the event of an emergency.

No. 4: The best way to keep a secret? Keep it to yourself.

To avoid accidentally spilling private details, don’t say them at all.

The rest of the rule goes even further: “Second best? Tell one other person — if you must. There is no third best.”

As with the rest of their training, McGee, Special Agent Nicholas Torres (Wilmer Valderrama) and the others were taught to stay tight-lipped about what they saw on duty and how it affected their courses of action.

No. 9: Never go anywhere without a knife.

Similar to rule No. 2, this piece of advice is not only about preparation, but also self-defense.

Though the NCIS team members are usually armed, backup can go a long way if things go wrong. A knife can be used as both a weapon and a tool to help get out of tricky situations.

No. 12: Never date a coworker

Things get messy when personal and professional lives mix.

As viewers have seen, a few team members have gotten romantically involved with each other over the years, like DiNozzo and Special Agent Ziva David (Cote de Pablo); Torres and Special Agent Eleanor Bishop (Emily Wickersham); and more recently, Palmer and Special Agent Jessica Knight (Katrina Law).

Gibbs’ rule to never date a co-worker was implemented to avoid drama in the office, but even he had a hard time following it. Each relationship played out with a varying degree of complication, including broken hearts.

No. 14: Bend the line, don’t break it

Different situations have unique boundaries of what’s acceptable, but remember to bend the rules, never break them.

The rule was introduced in season 11 of NCIS but is still an important mantra years later. Notably, an October 2024 episode of the prequel series, NCIS: Origins, is titled “Bend, Don’t Break.”

No. 28: When you need help, ask.

Asking teammates for help is not a sign of weakness; instead, it can strengthen the bond between NCIS members.

Whether it’s a case that continuously leads to more questions than answers or a personal dilemma someone can’t shake, Gibbs’ team looks toward one another for assistance when all else fails.

No. 35: Always watch the watchers

Despite upholding their own standards, Gibbs also encouraged his agents to keep tabs on the organizations and/or individuals meant to oversee others. Doing so could help avoid massive mistakes in the future.

No. 36: If it feels like you’re being played, you probably are

In addition to the training the agents received, they were always reminded to return to the basics, including trusting their instincts. If things seem suspicious or too good to be true, they probably are.

No. 51: Sometimes you’re wrong.

Occasionally, it’s more important to admit an error than cling to the belief that you’re always right.

Another essential rule, so crucial that the NCIS season 7 finale was titled, “Rule Fifty-One.”

No. 91: When you decide to walk away, never look back

To put it simply, leave the past in the past. Don’t obsess over what could have been and move on.

A rule that Gibbs lives by, so much so that he named his boat Rule 91. In the season 18 finale, “Rule 91,” Gibbs’ boat was blown up, but he swam to safety.

In the next season, Gibbs followed his own rule and left NCIS, choosing to stay and live in Alaska, where he was last seen fishing.