Under Section 13 of the Water (Prevention and Control of Pollution) Act, 1974, a Joint Board is a combined Pollution Control Board formed by the Central Government for two or more States, or for one or more States and a Union Territory, where it is in the public interest to do so. It exercises the powers and functions of the State Boards in the concerned States/Union Territories.

The Joint Board's composition mirrors that of the Central Pollution Control Board — a Chairman plus members representing Central and State governments, with a full-time Member Secretary, not exceeding 17 in total. It ensures coordinated pollution control in regions that share river basins or ecological zones across state boundaries.