Tim writes Rule #39 on the type writter

A capture from episode 10 of season 12 - a particularly rules heavy Christmas episode.

The rules

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, S08xE11, McGee tells Agent Borin that rule number one has been taken twice, showing that he knows that there are two number one rules.

McGee revisits this set of rules in S12xE10:

Tony: Anything to close this case and open my vacation so go get your binary buddies to cough up some info, will you?
McGee: Even if it means breaking rule number one?
Tony: Which one?
McGee: Both. Never put your suspects together, and never screw over
your partner.

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" 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.

Rule #8: Never take anything for granted. 

Note: This is re-quoted as "Never assume." by McGee to Gibbs six years later.

Rule #9: Never go anywhere without a knife.

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 #13: Never, ever involve a lawyer.

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 #22: Never, ever bother Gibbs in interrogation.

Rule #23: Never mess with a Marine's coffee... if you want to live.

Rule #27: There are two ways to follow someone. First way, they never notice you. Second way, they only notice you.

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 #62: Always give people space when they get off the elevator.

Rule #69: Never trust a woman who doesn't trust her man.

Gibbs Unnumbered Rules

• "Never date a woman that eats more than you do." - Singled Out, but Tony said it.
• 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 6x15. 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 rules

Gibbs' counterpart at CGIS, also has a set of rules. For now only one has surfaced.

#1: Never make excuses.

McGee rules

Rule #1 Never lie to Gibbs.

Rule #70 Keep digging until you hit bottom
Quoted by McGee in episode 5 of season 12 during his "McGibbs" transformation

DiNozzo rules

Rule #1: Don't sit on the sidelines while your people are in trouble.

Rule #3: Never underestimate your opponent.

Abby's rules.

Rule #1: Do not lie to Abby.

Rule #9: Always keep a spare

Jimmy Palmer Rules

Jimmy's Rule #1: Pipettes can never be too clean.