From the RHP games explorer:
Also called the Queen's Fianchetto Opening, it is named after the Danish Grandmaster Bent Larsen. Larsen was inspired by the example of the great Latvian-Danish player and theoretician Aron Nimzowitsch (1886-1935), who often played 1.Nf3 followed by 2.b3, which is sometimes called the Nimzowitsch-Larsen Attack.
The opening move 1.b3 prepares to fianchetto the queen's bishop where it will fight for the central squares and point towards Black's kingside. Still, 1.b3 is less popular than 1.g3 (Benko's Opening), which prepares a quick kingside castling. According to ChessBase, 1.b3 ranks sixth in popularity out of the possible twenty first moves while the fifth-ranking 1.g3 is about three times as popular.
Although Bent Larsen was initially very successful with this opening, Larsen's Opening suffered a setback in the 1970 USSR vs. Rest of the World match in Belgrade. There, Larsen lost with this opening against Boris Spassky in just 17 moves, a remarkably quick loss, especially when playing White. Larsen was also decisively defeated when playing this opening against Balinas at Manila 1975.
It is classified under the A01 code in the Encyclopaedia of Chess Openings.
This text has been taken from Wikipedia.