Watch SNL's first promo of Season 45 with Woody Harrelson and Billie Eilish

Saturday Night Live takes on a back-to-school theme for Eilish's first visit to the iconic TV show, which Harrelson will host for the fourth time on Saturday. ALSO: Watch the best of Harrelson on SNL from his past hosting stints in 1989, 1992 and 2014.