By season 20 (2010), Giuliani and Bloomberg have sanitized the streets. The detectives use laptops. The Twin Towers are a void in the skyline. The villains are hedge fund managers and corrupt politicians, not street-corner drug dealers. The show changed because New York changed. Few series have ever been such a faithful mirror of their setting. Why do we still care? Because Law & Order believed in something radical: that institutions, however flawed, are worth defending. Jack McCoy lost cases. Briscoe got the wrong guy sometimes. Van Buren battled cancer and departmental racism. But every single week, they showed up. They did the work. They read the suspect their rights. They filed the motion. They made the argument.

From September 13, 1990, to May 24, 2010, Law & Order didn’t just air on NBC. It occupied a permanent address in the national psyche. The "mothership"—as fans call it to distinguish it from its sprawling progeny ( SVU , Criminal Intent )—delivered 456 episodes of pure, procedural poetry. Over 20 complete seasons, it perfected a formula so rigid, so reliable, and so unexpectedly brilliant that it became the longest-running primetime drama in television history (until its own spin-off broke the record).

By A Television Critic