Solo climbing or soloing is a style of climbing in which the climber climbs alone, without somebody belaying him. There are two ways to climb solo: it can be performed with the safety of a rope and a self-locking device, in which case it is a form of aid climbing called roped soloing or it can be done without any rope or other form of protection in which case it is a form of free climbing called free soloing.

Free soloing is considered the purest form of climbing but is also the most dangerous. It is mostly practiced on routes that are familiar to the climber and where its difficulty lies well below the climber's abilities. However, inherent risks such as loose rocks or sudden change in weather are always present and fatalities are not unknown to the practice. Free soloing belongs to the group of extreme sports.

Free soloing on seacliffs, where a climber falling into deep water may avoid injury, is known as deep water soloing.