Matti Yrjänä Joensuu (31 October 1948, Helsinki, Finland – 4 December 2011, Valkeakoski, Finland) was a Finnish writer of crime fiction.
He has been awarded the State's Literature Prize (1982), Vuoden johtolanka prize (1985, 1994, 2004), and he has been nominated for two Finlandias.
He received the Martin Beck Award in 1987.
Joensuu's Harjunpää stories have also been adapted for Film & TV.
Joensuu's work has been translated into English, Bulgarian, Dutch, Italian, Norwegian, French, Swedish, German, Slovak, Danish, Hungarian, Armenian, Russian and Estonian.