The Seveso disaster was an industrial accident that occurred around 12:37 pm July 10, 1976, in a small chemical manufacturing plant approximately 15 km (9.3 mi) north of Milan in the Lombardy region in Italy. It resulted in the highest known exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in residential populations which gave rise to numerous scientific studies and standardized industrial safety regulations. The EU industrial safety regulations are known as the Seveso II Directive.

The Seveso disaster was so named because Seveso, with a population of 17,000 in 1976, was the community most affected. Other affected neighbouring communities were Meda (19,000), Desio (33,000), Cesano Maderno (34,000) and to a lesser extent Barlassina (6,000) and Bovisio-Masciago (11,000). The industrial plant, located in Meda, was owned by the company ICMESA (Industrie Chimiche Meda Società Azionaria), a subsidiary of Givaudan which in turn was a subsidiary of Hoffmann-La Roche (Roche Group). The factory building had been built many years earlier and the local population did not perceive it as a potential source of danger. Moreover, although several exposures of populations to dioxins had occurred before, mostly in industrial accidents, they were of a more limited scale.

Seveso (in Lombard language: Séves) is a town and comune in the Province of Monza and Brianza, in the Region of Lombardy. The economy of the town has traditionally been based around the furniture industry.

Its name comes from the river of the same name which crosses the comune in a north-south direction.

Seveso received the honorary title of city with a presidential decree on June 18, 2003.

The town is situated 21 km to the north of Milan in the Brianza lowlands. The territory of the commume is highly urbanised, with the majority of inhabitants living in the town.

Seveso lies on the national trunk road Statale dei Giovi, which connects Milan to Como and on the Milan-Meda motorway. It is also serviced by the Milan–Asso railway line.

Neighbouring communes are Meda, Seregno, Barlassina, Cogliate, Cesano Maderno.

Seveso's origins date back to about the 3rd century BC, when certain areas around Brianza were used as military staging posts for the Roman conquest of Gaul. Towards 780, the monastery at Meda was founded, the jurisdiction of which extended to the territory of Seveso.