There are basically two kinds of water vapour explosions, viz. confined and unconfined. Confined explosions can occur in various situations in industry. Unconfined explosions typically occur when very hot molten metal accidentally makes contact with water. In order to explain the extremely rapid production of water vapour that can then occur, "fine fragmentation" of the molten metal must take place. The paper first presents some early suggestions for the nature of the fine fragmentation process. In more recent theories the Weber number, We; is used as a measure of expected extent of molten-metal fragmentation in a given situation. Film boiling plays a central role. Attempts at developing mathematical models of unconfined water vapour explosions have been made. The next section of the paper is devoted to case histories of unconfined water vapour explosions. Then various kinds of confined water vapour explosions are discussed, including water boiler explosions, water vapour BLEVEs, and water vapour explosions in the paper industry. Some case histories of confined water vapour explosions are also given. The final section of the paper is devoted to measures for preventing and mitigating water vapour explosions in industry. (C) 2015 Elsevier Ltd. All rights reserved.