· over the years, ncis viewers have learned about dozens of the rules that leroy jethro gibbs lives by. Gibbs rules are an extensive series of guidelines that former nis /ncis special agent leroy jethro gibbs lives by and teaches to the people he works closely with. Weve got a complete list for you. Heres what to know about gibbs rules and the meanings behind them. But what are leroy jethro gibbs rules ? Never let suspects sit together. · leroy jethro gibbs has a set of rules he lives by. Heres the complete list to date of gibbs rules. · gibbs rules are back thanks to ncis: · if you’re going to be on gibbs ’ (mark harmon) team on ncis, live by these. For the last 17 years, the ncis writers have been teasing us and releasing a few rules each year. Mark harmon played the character for nearly two decades on the series, using the rules to help establish his character and how the naval criminal investigative service operated. · understanding all of gibbs rules in ncis and what they mean is essential to knowing leroy jethro gibbs. · mark harmon left the series in season 19, but his characters life advice lives on years later. Never screw over your partner. Heres a rundown of every rule that gibbs has mentioned.