In the literary world, Bosch is the half brother of Michael (Mickey) Haller from The Lincoln Lawyer (2011). They have same father; also a lawyer named Michael Haller. Michael Jr is the legitimate son, while Harry Bosch is illegitimate.
Exists in the same universe as Bloodwork, with Clint Eastwood. Eastwood's character, Terry McCaleb, was an FBI agent who had intersected with Bosch, and Bosch's ex-wife Eleanor Wish (who is also an ex-FBI agent) in earlier cases.
Jamie Hector and Lance Reddick were both actors in the Wire. Lance Reddick were acting a high ranking police officer in both Bosch and the Wire. Jamie Hector on the other hand, was acting as a drug lord in the Wire, and a detective in Bosch.
The trivia item below may give away important plot points.
Lou Escobar, the assistant DA killed by Raynard Waits in making his escape, was also the name of Jake Gites former police department partner in the movie Chinatown, which also took place in Los Angeles.