Koski holds a Master's degree in Communications and Sociology (University of Tampere, Finland). He is editor of the Finnish cinema magazine Filmihullu and lecturer at the Lahti Polytechnic Institute of Design in Finland. Koski has published several Finnish-language books on Finnish popular culture, including Olavi Virta (1878, with Peter von Bagh and Pekka Aarnio), Armin vuodet (1982, with Leo Linsten), Alemmat taiteet (1985), The Beatles (1986), Sorsa-diagnoosi (1989), Lööppikirja (2000, with Peter von Bagh), and Julkisia eläimiä (2001).