Crystals of Ba2TiP2O9were grown from the melt by the Bridgman technique. Two types of twinning occur, namely: growth twins and mechanical twins. The growth twins form with the (100) plane as the twin plane and mechanical twins form with the (001) plane as the twin plane. In twinned crystals, growth proceeds most rapidly in the [010] direction. Rapid growth in this direction is believed to result from efficient nucleation at the re‐entrant corners formed by the ⟨310⟩ faces of the twin components. The mechanical twins form according to pseudo‐merohedral symmetry by reflection across the (001) twin plane. The angle of obliquity is 4° and the twinning shear is 0.140.