Throughout the CSI franchise’s 39 seasons and 838 episodes, there have been plenty of memorable moments, but the one that stands out the most happens over the course of three episodes. The CSI franchise debuted in October 2000 when CSI: Crime Scene Investigation premiered, and it quickly became a hit. Millions of people watched the CSI show, inspiring CBS to expand its universe. Its success resulted in the network ordering the first spinoff, CSI: Miami, in 2002, and the second one, CSI: NY, in 2004. CSI was a cultural phenomenon that forever changed the course of TV (in numerous respects).

https://screenrant.com/csi-trilogy-crossover-episode-franchise-peaked-shared-universe-op-ed/