Ling Woo (Lucy Liu) wasn't originally intended to be a regular, but David E. Kelley liked her so much as a guest star, he and the writer decided to reveal that she has a law degree and join the firm after a few episodes, giving her a reason to be there.
Ally McBeal (1997) takes place in the same world as David E. Kelley's other television series The Practice (1997). Guest star Dylan McDermott appeared in the crossover episodes Ally McBeal: The Inmates (1998) and Ally McBeal: These Are The Days (1998) as his character "Bobby Donnell". The Practice (1997) premiered six months before Ally McBeal (1997).
The trivia item below may give away important plot points.
In an effort to boost ratings, Robert Downey, Jr. was hired to play Ally's love interest at the start of season four. The ratings increased and David E. Kelley began planning to have that season end with the wedding between Ally and Robert Downey, Jr.'s character. However, before production on the season finale could begin, Downey was arrested on a drug-related charge. Despite objections from David E. Kelley, Fox fired Downey from the show and forced Kelley to have to re-write a brand new season finale episode that removed the Larry Paul character from the series, and re-write and re-shoot a new ending to the previous episode, so as to remove all references to the aborted wedding storyline. Ironically, the episode's title remained "The Wedding".