Mount Pinatubo (Sambal: Bakil nin Pinatobo; Kapampangan: Bunduk/Bulkan ning Pinatubu, Bunduk ning Apu Malyari; Pangasinan: Palandey/Bulkan na Pinatubu; Ilocano: Bantay Pinatubo; Tagalog: Bundok/Bulkang Pinatubo IPA: [pinɐtubɔ]) is an active stratovolcano in the Zambales Mountains, located on the tripoint boundary of the Philippine provinces of Zambales, Tarlac and Pampanga, all in Central Luzon on the northern island of Luzon. Its eruptive history was unknown to most before the pre-eruption volcanic activity of early 1991. Pinatubo was heavily eroded and obscured from view by dense forests which supported a population of several thousand indigenous Aetas.

Pinatubo is most notorious for its VEI-6 eruption on June 15, 1991, the second-largest terrestrial eruption of the 20th century after the 1912 eruption of Novarupta in Alaska.

Complicating the eruption was the arrival of Typhoon Yunya, bringing a lethal mix of ash and rain to towns and cities surrounding the volcano. Predictions at the onset of the climactic eruption led to the evacuation of tens of thousands of people from the surrounding areas, saving many lives. Surrounding areas were severely damaged by pyroclastic surges, pyroclastic falls, and subsequently, by the flooding lahars caused by rainwater re-mobilizing earlier volcanic deposits. This caused extensive destruction to infrastructure and changed river systems for years after the eruption. Minor dome-forming eruptions inside the caldera continued from 1992 to 1993.

The effects of the 1991 eruption were felt worldwide. It ejected roughly 10 billion tonnes (1.1×1010 short tons) or 10 km3 (2.4 cu mi) of magma, and 20 million tonnes (22 million short tons) of SO2, bringing vast quantities of minerals and toxic metals to the surface environment. It ejected more particulate into the stratosphere than any eruption since Krakatoa in 1883. Over the following months, the aerosols formed a global layer of sulfuric acid haze. Global temperatures dropped by about 0.5 °C (0.9 °F) in the years 1991–1993, and ozone depletion temporarily saw a substantial increase.