A removable surfboard fin adapter that allows removable fins, fin boxes and fin systems from different manufacturers to be compatible with each other. A two-tabbed type removable surfboard fin is received and secured in the recess of a single-tab type surfboard fin receiving box that would not otherwise be able to receive and secure a two-tabbed type removable surfboard fin. The adapter includes two slots that accept the tabs of the two-tabbed fin. The front, rear, or both front and rear of the adapter include a notch for securing he adapter to the single-tab receiving box. Angled slots are provided for canted fins.