A pipeline breakaway coupling (10) comprising a pair of valve housing members (12,14) fixedly attached to each other by means of one or more breakaway coupling members (16). The valve housing members (12,14) define a hollow bore (18) along which flowable material may flow and the breakaway coupling members (16) permit the valve housing members (12,14) to separate from each other when exposed to a tensile load exceeding a predetermined limit.An end cap (26) releasably connected to each valve housing member (12,14) to allow connection of the valve housing members (12,14) to respective inlet and outlet pipelines.A valve cassette (20) is releasably retained between each valve housing member (12,14) and the respective end cap (26). Each valve cassette (20) includes a valve member (22) movable between a valve open position and a valve closed position. The valve member (22) when at its valve closed position being sealingly engaged with a valve seat (24) formed in respective valve housing member (12,14), thereby closing the hollow bore in the respective valve housing member (12,14). Each valve member (22) is biased to move to its valve closed position on separation of the valve housing members (12,14).