During season 3, Kathryn Erbe's character Eames was temporarily written out as serving as a surrogate mother for her sister-in-law, mirroring the fact that Erbe herself was pregnant with her second child at the time.

In season 7, Julianne Nicholson's character Megan Wheeler was sent to Europe as a plot device to cover Nicholson's real-life pregnancy leave, with Alicia Witt brought in temporarily to play Detective Nola Falacci.

Chris Noth first reprised his original Law & Order role of Detective Mike Logan as a guest appearance in the fourth season, which led to him joining the Criminal Intent cast as a co-lead starting in season five.

Several original Law & Order cast members appeared in character during the first season, including Jerry Orbach and Jesse L. Martin in 'Poison', S. Epatha Merkerson in 'Badge', and J.K. Simmons in 'Crazy'.

Leslie Hendrix recurred throughout the series reprising her Law & Order role as Medical Examiner Dr. Elizabeth Rodgers, starting with the first-season episode 'The Faithful'.

Kathryn Erbe later reprised her role as Alexandra Eames in two episodes of Law & Order: Special Victims Unit's fourteenth season, with her character having transferred to a Homeland Security task force.

The show's on-set lighting and visual style changed noticeably over the run: it was very dim during the first five seasons, brightened in season six, and at the start of season nine the production removed sections of the squad room ceiling and added incandescent lighting strips to give it a warmer look, alongside a switch from 35mm film to digital video acquisition.

Due to content issues stemming from the season 8 episode 'The Glory That Was...', only 15 of that season's 16 episodes were included in the Region 1 DVD release.

The show was adapted internationally, including a French version produced by TF1 Alma Productions set in Paris that ran for 20 episodes from 2007 to 2008, and a Russian version filmed in Moscow that became one of Russia's top-rated series, expanding from an initial order of 8 episodes to around 40.