Mikko Simo Yrjänä Leinonen (born July 15, 1955 in Tampere, Finland) is a retired Finnish Ice hockey player and currently the chief executive of Finnish elite league SM-liiga team Tappara. He played 162 games in the National Hockey League for the New York Rangers and Washington Capitals, scoring 31 goals and 78 assists.
He played for Tappara Tampere from 1973 to 1977, winning the league championship in 1975. He also played for Finland at the 1974 and 1975 World Junior Championships. In 1977 he moved to MODO Hockey in Sweden for two seasons and then back to Finland to play for Kärpät Oulu for two seasons until 1981.
During that time he played for Finland in the 1978, 1979, and the 1981 World Championships. Leinonen competed for the Finnish team in the 1980 Winter Olympics and scored an impressive 3 goals and 3 assists during that tournament.
The New York Rangers signed Leinonen as a free agent in 1981. He scored 31 points for them in 1981-82 and then 51 in 1982-83. The following season (1983-84) he started out in the minors but returned to finish the season with the Rangers.
Leinonen's largest claim to fame is sharing the NHL record for most assists in one playoff game with Wayne Gretzky, each with 6.