Per Fredrik Wahlöö (5 August 1926 – 22 June 1975) – in English translations often identified as Peter Wahloo – was a Swedish author. He is perhaps best known for the collaborative work with his partner Maj Sjöwall on a series of ten novels about the exploits of Martin Beck, a police detective in Stockholm, published between 1965 and 1975. In 1971, The Laughing Policeman (a translation of Den skrattande polisen, originally published in 1968) won an Edgar Award from the Mystery Writers of America for Best Novel. Wahlöö and Sjöwall also wrote novels separately.
Wahlöö was born in Tölö parish, Kungsbacka Municipality, Halland. Following school, he worked as a crime reporter from 1946 onwards. After long trips around the world he returned to Sweden and started working as a journalist again.
He had a thirteen-year relationship with Sjöwall but they never married, as he already was married. Both were Marxists.