The Greycliffe disaster occurred in Sydney Harbour (Australia) on 3 November 1927 when the harbour ferry Greycliffe and the Union Steamship Company mail steamer Tahiti collided. The smaller ferry was cut in two and sank with the loss of 40 lives, the deadliest incident on Sydney Harbour.

Sydney Harbour ferry services date back to the first years of Sydney's European settlement. Slow and sporadic boats ran along the Parramatta River from Sydney to Parramatta and served the agricultural settlements in between. By the mid-1830s, speculative ventures established regular services. From the late-nineteenth century the North Shore developed rapidly. A rail connection to Milsons Point took alighting ferry passengers up the North Shore line to Hornsby, New South Wales via North Sydney. Without a bridge connection, increasingly large fleets of steamers serviced the cross harbour routes and in the early twentieth century, Sydney Ferries Limited was the largest ferry operator in the world.