From its gritty documentary look to its signature note-knocking "tching-tching" that signals scene changes, Law & Order was a groundbreaking cop show when it debuted in 1990. It is television's most resilient series, surviving huge changes to its ensemble. One of the secrets of the show's durability is its compelling structure. The first half of each hour-long episode is a classic police procedural in which "Law", personified in the first season by partners Greevey (George Dzundza) and Mike Logan (Christopher Noth) investigate a crime and make an arrest. The second half chronicles the ensuing trial, as prosecuted by assistant district attorneys Ben Stone (Michael Moriarty) and Paul Robinette (Richard Brooks) under the supervision of Steven Hill's Adam Schiff (more feisty and animated here than in later seasons).

Law & Order is also distinguished by its superb writing. Several episodes take their inspiration from the headlines, including "By Hooker, By Crook" (about a socialite-run call-girl ring) and "Indifference", which recalls the tragic Lisa Steinberg child abuse case. Others deal with such hot-button issues as abortion ("Life Choice") and AIDS ("The Reaper's Helper"). Another plus is the talent pool of character actors who lend their verisimilitude. Guest stars include Samuel L Jackson and Philip Seymour Hoffman ("The Violence of Summer"), The West Wing's John Spencer ("Prescription for Death"), Sex and the City's Cynthia Nixon ("Subterranean Homeboy Blues") and The Sopranos' Dominic Chianese ("Sonata for Stolen Organ"). --Donald Liebenson