Lines of Action (or LOA) is a strategy board game for two players invented by Claude Soucie. The objective is to connect all of one's pieces into a single group.

The game was recommended by the Spiel des Jahres in 1988.

The game was given wide dissemination and positive publicity by its inclusion in Sid Sackson's book A Gamut of Games (1969), but for many years no stable playing community developed to explore the strategy to any depth. Only starting in the 1990s has any deep understanding of the game evolved.

In the last few years, not only has the play of the best humans risen dramatically, but simultaneously excellent computer programs have emerged. The level of play is improving both among humans and computers, but for the present the strongest LOA-playing entity in the world is the program MIA. MIA took first place in the 8th Computer Olympiad (2003), 9th Computer Olympiad (2004) and 11th Computer Olympiad (2006).

The Lines of Action world championships are held annually as part of the Mind Sports Olympiad, see below. Other notable players include Jorge Gómez Arrausi and Gianfranco Buccoliero (winner of the largest loa tournament to date). Jorge has played competitive games against top computer programs, but has not been triumphant in recent matches.