Maurice "Mo" Johnston (born April 30, 1963 in Glasgow) is a Scottish soccer forward, who made his name with Celtic before controversially playing with Rangers.

Johnston started his career in 1981 with Partick Thistle and scored 41 goals in two and a half seasons there. He then moved on to English club Watford; 23 goals in a season and a half and a trip to the FA Cup final earned Mo a contract with Scottish giants Celtic, the club he supported as a boy. Embraced by the club's fans, Johnston would score 55 goals in his three years there.

Mo made his debut with the Scottish national team in 1984, and retired from international competition in 1992, after scoring 14 goals in 38 caps. He played in the 1990 World Cup, scoring against Sweden, and is widely considered one of Scotland's best striker of the 1980s.

Johnston moved on to French club Nantes in 1987 and scored 22 goals in two seasons there; it was his return from France that spun controversy. After first claiming he will never return to Scotland to play, he reconsidered, saying "Celtic are the only team I want to play for". But it was not Celtic he signed with, but their biggest rivals, Rangers. For that, he was branded Judas by Celtic fans. Although it is often said that Johnston was the first Catholic to sign with Rangers since World War II, that is not the case; John Spencer signed with the team in 1985. Since Spencer did not play with the first team until after Mo came aboard, it is possible that Johnston was the first Catholic to play for Rangers since World War II, but that is debatable as well. Since Johnston's signing, Rangers play considerably more Catholics than they had done previously, this probably has more to do with playing non-Scots, rather than a lifting of any alleged ban on Catholic players.

Mo scored 36 goals for his new club, leading them to the first three of nine consecutive Scottish titles. In 1991, he moved to English club Everton, scoring ten goals in two seasons. Johnston came back to Scotland with Hearts and then Falkirk, scoring just five and six goals respectively in season and a half with each club.

Johnston made the switch to the United States and Major League Soccer in 1996, signing with the Kansas City Wiz (later Kansas City Wizards). He would score 31 goals in 149 games for the club, adding a goal in 15 playoff games. Moving to the midfield as the years went by, Johnston was the glue on the Wizards team that won the MLS Cup in 2000.

He retired after the 2001 season, and from 2003 on has been an assistant coach to Bob Bradley for the MetroStars.