|In-line style||With references|
Gibbs' Rules are an extensive series of guidelines that Leroy Jethro Gibbs lives by and teaches to the people he works closely with.
Gibbs's rules originated from his first wife, Shannon Gibbs, who told him at their first meeting, "Everyone needs a code they can live by." Years later, after their wedding, Gibbs began writing his own rules down, keeping them in a small tin inside his home. Though he uses it often we almost never see the tin.
The knowledge of the rules' origins is left as a mystery to the people that Gibbs works with, though some of them do make concentrated efforts to find out. Tony makes several attempts to find out who taught Gibbs the rules, though he has not yet met with any success. On one occasion, he quoted Rule Nine as a rule that "they teach you in the Marine Corps," but the Marine in question was unaware of what he was referring to. On another occasion, Tony asked Jackson Gibbs if he had taught the rules to his son, but the older man denied any involvement.
At the beginning of her tenure with NCIS, Gibbs informed Ziva David that there were approximately fifty rules, and that it was his job to teach them to her. Some years later, Gibbs added the fifty-first rule to the tin he kept the rules in. According to Tony, seven of the rules directly concern lawyers, and the eighth rule was inspired by a lawyer. Rule forty and above are not rules necessary for everyday life, they are for emergencies.  Note: Look below for info about rules # 1-3
Rule #1: Never let suspects stay together.This is the first rule of investigation not a real Gibbs rule.
Rule #1: Never screw over your partner. Note: This is quoted by McGee to be Gibbs' Number One, but the other Rule One is quoted in other episodes to be his. In Ships in the Night, S8 E11, McGee tells Agent Borin that rule number one has been taken twice, showing that he knows that there are two number one rules.
Rule #2: Always wear gloves at a crime scene.
Rule #3: Don't believe what you're told. Double check.
Rule #3: Never be unreachable. (*Most likely one of Mike Franks' "Golden Rules" (see below) as opposed to Gibbs, because Gibbs has been known to intentionally be unreachable.*) This was a rule quoted by Tony regarding Ziva or Tim
Rule #4: The best way to keep a secret? Keep it to yourself. Second best? Tell one other person - if you must. There is no third best.
Rule #5: You don't waste good. 
Rule #6: Never say you're sorry. It's a sign of weakness. Note: This is continuously told to Tony, Ziva and Tim through a smack to the back of their heads.
Rule #7: Always be specific when you lie.
- Sometimes listed as "Never leave home without a knife."
- Also quoted as "Always carry a knife."
Rule #10: Never get personally involved in a case.
- Said by the SecNav to be Rule #1 in Washington politics.
Rule #11: When the job is done, walk away.
Rule #12: Never date a co-worker.
Rule #15: Always work as a team.
Rule #16: If someone thinks they have the upper hand, break it.
Rule #18: It's better to seek forgiveness than ask permission.
Rule #23: Never mess with a Marine's coffee... if you want to live.
Rule #35: Always watch the watchers. 
Rule #36: If you feel like you are being played, you probably are.
Rule #38: Your case, your lead.
Rule #39: There is no such thing as coincidence.
DiNozzo says "There is no such thing as a small world" is 39a in 10x14 "Canary"
Rule #40: If it seems someone is out to get you, they are.
Rule #42: Never accept an apology from someone who just sucker punched you.
Rule #44: First things first, hide the women and children.
Rule #45: Clean up the mess that you make.
- Also stated as, "Never leave behind loose ends."
Rule #51: Sometimes - you're wrong.
- This is written on the back of the card with Rule 13 (which Gibbs circles first) in the tin where Gibbs keeps the rules. It is unknown if his coworkers are aware of this rule.
Rule #69: Never trust a woman who doesn't trust her man. 
- In my country, on my team, working my cases, my people don't bypass the chain of command.
- The "Unspoken Rule" (Franks): You do what you have to do for family. (Season 8 Episode 1)
- Don't work the system when you can work the people.
- Don't stop checking and rechecking evidence until you are satisfied.
- If you want to find something, you follow it. (Said by Gibbs to Mike Franks in "Deliverance," Episode 6.15. Gibbs then added, "I learned that one from you, Mike.")
- Besides Rule 13, Gibbs has 6 other rules involving lawyers, but, according to DiNozzo, "You only need to know number 13; it's the umbrella one."
- Never second guess yourself in a relationship and life.
- Abigail Borin, Gibbs' counterpart at CGIS, also has a set of rules. The only one currently known is her Rule #1: Never make excuses. (Ships in the Night).
- McGee has formed his own set of rules. Only 1 is known:
- Rule #1 Never lie to Gibbs.
- When DiNozzo was in charge, he made a set of rules.
- Rule #1: Don't sit on the sidelines while your people are in trouble.
- Rule #3: Never underestimate your opponent.
- Abby also has her own rules.
- Rule #1: Do not lie to Abby.
- Rule #9: Always keep a spare.
- Jimmy Palmer once had a rule.
- Jimmy's Rule #1: Pipettes can never be too clean.
Although Gibbs has his list of rules to live by, he does not always adhere to them. One example is Rule #3. When Gibbs does not wish to be reached, he has been known to leave his cell phone behind. Except that many believe that to be one of Frank's rules since there are two Rule #3's. The other being 'Don't believe what you're told. Double check.' ... Which sounds more like Gibbs. Also, on the anniversary of his last marriage, he unplugged his home phone and dropped his cell phone in paint thinner after his ex-wife began harassing him with phone calls. Gibbs also admits that rule number 10 is the one that he has had the most "trouble with."
Gibbs broke Rule #1 (Never let suspects stay together) on Ships in the Night (Season 8) in order to get a confession. This also occurred in Caught on Tape, but the suspects turned out to be innocent. Additionally, Gibbs broke the rule in A Man Walks into a Bar, but the suspects were only guilty of covering up suicide, not murder.
Gibbs also broke Rule #12 with former NCIS Director and partner in Europe, Jenny Shepard. Jenny was Gibbs' probie in their Europe missions and became romantically involved, which was ended by Jenny so she could lead her own team in Madrid. Although, since the relationship ended badly, some people suspect that this rule was created because of this relationship.
Another exception that Gibbs sometimes makes concerns Rule #6. Though Gibbs constantly tells people around him to never apologize, that it is a sign of weakness, he himself has apologized on at least six occasions:
- To Caitlin Todd for being late to her funeral.
- To Donald Mallard following his return from Mexico.
- To Joann Fielding for not being able to protect Shannon Gibbs and Kelly Gibbs.
- To Abigail Sciuto for frightening her and not being able to tell her what she wants to hear.
- To the victim's lover for her loss, although he originally believes that she was being selfish (A Man Walks Into A Bar...)
- To Timothy McGee for not being with him when he was accused of shooting a cop
- To "The General" (Captain Wescott) in Shell Shock (Part 2) for making him face a former serviceman and teammate, in which the encounter went poorly. Gibbs said, "That was my bad," for making Westcott agree to the meeting.
- Though not shown, in Semper Fidelis ICE Agent Julia Foster-Yates claims that Gibbs and Fornell apologized to her for accusing her of murdering a coworker. McGee is shocked at the idea that either of them would apologize.
Gibbs also almost never accepts an apology from someone, preferring to simply offer correction to whomever made an error in an attempt to teach a lesson. One exception to this aspect of the rule was when McGee apologized concerning the situation with his sister, Sarah (Twisted Sister). Gibbs has also accepted some apologies because they are covered by rule #18: "It's better to seek forgiveness, than ask permission."
Also an apology isn't a sign of weakness if it's between friends, as Gibbs tells Dr. Mallard in Smoked.
Although not strictly an exception, Gibbs did add a sort of corollary to Rule 39 concerning coincidences. In Episode 3.15, Head Case, when Tony says, "We don't believe in coincidences around here," Gibbs added, "However, we do believe in bad luck."
Throughout the series, there have been two rules referenced as the first and third of Gibbs' rules. For some time, it was believed that the duplications were either continuity errors or that the list of rules was meant to be malleable. Eventually, however, Executive Producer Shane Brennan revealed that the duplication was actually intentional:
“Gibbs lives his life by a set of rules that took root from the first day he met Shannon. Over time, Gibbs added to the rules. When he joined NCIS, Mike Franks told him he didn't need dozens of different rules to be an agent... just three 'golden rules.' And this is why we have double ups on rules #1 and #3. Three of them are Gibbs' rules; three of them are Mike Franks’ rules. We are still to reveal the double-up on rule #2. And it's up to the fans to guess which of the rules were Mike Franks’ three golden rules and which were Gibbs'.”  In spite of this, however, Franks seems to know Gibbs' rules as well as anyone, as evidenced in the episode "Patriot Down" when Gibbs passed the message "Rule #44" (First things first: hide the women and children) to him through Camilla.
While most of the rules are for everyday use, Gibbs' rules 40-49 are considered emergency rules, to be invoked only in the most dire of circumstances.  When Gibbs told Abby that rule 40 was in play, and Abby told Tony, he took it to mean that "something unspeakably bad is going down."
Notes and References
- Season 6, Episode 4, Heartland. The only rule of Shannon's personal code that is quoted is either her first or third: "Never date a lumberjack."
- Season 7, Episode 24, Rule Fifty-One.
- Season 1, Episode 20, Missing.
- Season 2, Episode 9, Forced Entry.
- Season 3, Episode 4, Silver War.
- Season 6, Episode 7, Collateral Damage.
- Season 1, Episode 1, Yankee White.
- Season 4, Episode 14, Blowback.
- Season 9, Episode 17, Need to Know.
- Season 8, Episode 11, Ships in the Night.
- Season 3, Episode 13, Deception. This rule is also shown in Season 7, Episode 24, Rule Fifty-One, in the background when Gibbs opens the box.
- Season 8, Episode 22, Baltimore
- Season 7, Episode 12, Flesh and Blood. This rule has been mentioned throughout the series, but only in this episode was it given a specific number. The rule is also a direct reference to John Wayne's catch phrase in She Wore A Yellow Ribbon (John Ford, Director). Wayne said: "Never apologize, mister, it's a sign of weakness." to subordinates in a military situation. Mark Harmon's career has paralleled John Wayne's. They both were quarterback of their southern California college football team, both went into acting. (Harmon's father, Tom Harmon, was a Heisman Trophy winner and actor & announcer as well.)
- Season 1, Episode 23, Reveille.
- Season 3, Episode 10, Probie.
- Season 9, Episode 21, Rekindled.
- Season 1, Episode 13, One Shot, One Kill.
- Season 7, Episode 21, Obsession.
- Season 9, Episode 1, Nature of the Beast.
- Season 6, Episode 24, Semper Fidelis.
- Season 1, Episode 15, Enigma.
- Season 5, Episode 5, Leap of Faith.
- Season 8, Episode 24, Pyramid.
- Season 4, Episode 10, Smoked.
- Note that Tony breaks Rule #22 during Season 9, Episode 19, The Good Son.
- Season 7, Episode 15, Jack Knife.
- Season 9, Episode 01, Nature of the Beast
- Season 6, Episode 16, Bounce.
- Season 7, Episode 22, Borderland.
- Season 9, Episode 16, Psych Out.
- Season 7, Episode 23, Patriot Down. This rule was mentioned in this episode, but did not receive a number until Season 7, Episode 24, Rule Fifty-One.
- Season 5, Episode 19, Judgment Day Part 2.
- Season 9, Episode 7, Devil's Triangle.
- Season 3, Episode 5, Switch. This is identified as a rule because when Ziva David asks in the same conversation, "Are there any more of these rules I should be aware of?" Gibbs replies, "About fifty of them."
- Season 1, Episode 2, Hung Out to Dry.
- Season 3, Episode 24, Hiatus Part 2.
- Season 3, Episode 22, Jeopardy.
- Season 7, Episode 16, Mother's Day.
- Season 3, Episode 2, Kill Ari Part 2.
- Season 4, Episode 9, Twisted Sister.
- Shane Brennan's explanation of the duplication of Rules #1 and #3.