Port Phillip or Port Phillip Bay is a horsehead-shaped enclosed bay on the central coast of southern Victoria, Australia. The bay opens into the Bass Strait via a short, narrow channel known as The Rip, and is completely surrounded by localities of Victoria's two largest cities — metropolitan Greater Melbourne in the bay's main eastern portion north of the Mornington Peninsula, and the city of Greater Geelong in the much smaller western portion north of the Bellarine Peninsula. Geographically, the bay covers 1,930 km2 (750 sq mi) and the shore stretches roughly 264 km (164 mi), with the volume of water around 25 km3 (6.0 cu mi). Most of the bay is navigable, although it is extremely shallow for its size — the deepest portion is only 24 m (79 ft) and half the bay is shallower than 8 m (26 ft). Its waters and coast are home to seals, whales, dolphins, corals and many kinds of seabirds and migratory waders.

Victoria is a state in southeastern Australia. It is the second-smallest state, with a land area of 227,444 km2 (87,817 sq mi); the second-most-populated state, with a population of over 6.7 million; and the most densely populated state in Australia. Victoria is bordered by New South Wales to the north and South Australia to the west and is bounded by the Bass Strait to the south, the Great Australian Bight portion of the Southern Ocean to the southwest, and the Tasman Sea to the southeast. The state encompasses a range of climates and geographical features from its temperate coastal and central regions to the Victorian Alps in the northeast and the semi-arid northwest.