Which episode is Sara Sidle's first credited appearance?

Sara Sidle's first credited appearance is in “Cool Change,” the second episode of CSI: Crime Scene Investigation. Jorja Fox joined the series as Sara after the pilot, establishing the character as a materials-and-elements specialist recruited to Gil Grissom's Las Vegas team.

“Cool Change” aired during the show's first season and introduced Sara as a recurring member of the crime-lab ensemble. Her scientific background and emotionally intense connection with Grissom became important parts of the series over time. She later became a regular cast member and one of CSI's longest-running characters.

A common mix-up is choosing “Pilot,” because Sara is central to the show's main cast in later seasons. However, the pilot predates her credited entry. “Who Are You?” is also associated with the early crime-lab team, but it is the sixth episode and is not Sara's debut. Sara eventually left and returned several times, but “Cool Change” remains the canonical first credited appearance.