This article is about a surfboard part, for the subculture see skateboarding.

In surfing, a skeg is a stabilizing fin located at the rear of the surfboard. It was invented in 1935 by Tom Blake . A skeg has the effect of keeping the board moving forward in a controlled manner.

Without any fins on a surfboard, there is a tendency for the board to side slip and rotate. To counter this problem early surfers would hang the toes of their back foot over the edge of the board to create a pivot point and thus setting the rail, stabilising the board. Once introduced, the fin revolutionised surfing, allowing surfers to direct the board's momentum and providing more balance whilst turning. The single fin, centrally located, remained unchanged until the late 70's when a second was added and popularised by Aussie Mark Richards The new Twin Fin set up allowed much more flowing carves to be performed, with Mark Richards dominating the world competitive scene from 1979 to 1983.

In 1980 another Australian was developing another set up which would again change the face of surfing. His name was Simon Anderson and by attaching a third fin, positioned centrally behind the twin fins, he created the Thruster set up. Today, most surfboards still use the same arrangment with its popularity arising from the combined ability for carving turns and providing control and drive.

In the late 90's removable fin systems were developed. These provided surfers with a the ability to alter the riding characteristics of a surfboard, by changing the size or number of fins used. Allowing each surfboard to the tweaked to match the surf conditions.