Indoor soccer or arena soccer is a form of five-a-side or six-a-side version of minifootball. It is derived from association football and adapted to be played in walled hardcourt indoor arenas. It differs from the FIFA-sanctioned indoor football sport of futsal.

Indoor soccer, as it is most often known in the United States and Canada, was originally developed in these two countries as a way to play soccer during the winter months, when snow would make outdoor play difficult. In those countries, gymnasiums are adapted for indoor soccer play. In other countries, the game is played in either indoor or outdoor arenas surrounded by walls, and is referred to by different names (such as "fast football" (futbol rapido) in Mexico, Futebol Society or showbol in Brazil, and "indoor football" (futbol indoor) in Spain).

Indoor soccer has different regulations from other versions of association football designed for indoor play, such as futsal and five-a-side football. Unlike futsal, which is played on wooden or ceramic surfaces, indoor soccer is played on synthetic turf (or, in the case of the British Masters Football variety, synthetic carpet). Indoor soccer courts are either delimited by walls or lines, and there are no player throw-ins.

FIFA, the body that oversees international association football competitions, does not sanction the synthetic turf version of indoor soccer, as it has developed its own code of indoor football (which they refer to as futsal).

Indoor soccer is most popular in the United States, Canada, and Mexico, with several amateur, collegiate and professional leagues functioning. While internationally less popular than futsal, indoor soccer is also played at the league level in many countries outside North America. The World Minifootball Federation (WMF) is the governing body of indoor soccer at the international level, having replaced the International Fast Football Federation (FIFRA).

The term minifootball, which was originally coined in Europe, has been adopted by the WMF as a standard international name for the sport.

Indoor soccer is played throughout the world. Currently, the international federation dedicated to promoting the sport is the World Minifootball Federation (WMF) based in Switzerland. The WMF replaced the International Fast Football Federation (FIFRA), which had been based in Mexico and later, the United States. There are also regional federations who govern the sport including: African Minifootball Federation (AMF), Asian Minifootball Confederation (AMC), Confederación Panamericana de Minifútbol (CPM), European Minifootball Federation (EMF), Oceania Minifootball Federation (OMF).

Before Futsal was overseen by FIFA, the first Futsal World Champion was held in São Paulo, Brazil. This competition took place in 1982 and was conducted by the FIFUSA (before FIFA). Brazil came in first in the first Futsal World Tournament (1982) and the second Futsal World Tournament (1985). FIFA overtook this championship in 1989 and renamed the competition the FIFA Futsal World Championship.