Pieter Winsemius (born 7 March 1942) is a retired Dutch politician of the People's Party for Freedom and Democracy (VVD) and businessman.

Winsemius semi-retired from active politics and returned to the private sector and the public sector and occupied numerous seats as a corporate director and nonprofit director on several board of directors and supervisory boards (World Wide Fund for Nature, Vereniging Natuurmonumenten, Stichting Max Havelaar, European Centre for Nature Conservation, Stichting Pensioenfonds ABP and the Energy Research Centre) and served on several state commissions and councils on behalf of the government (Organisation for Scientific Research, National Insurance Bank, Staatsbosbeheer, Meteorological Institute and the Scientific Council for Government Policy).

Winsemius was appointed again as Minister of Housing, Spatial Planning and the Environment in the caretaker Cabinet Balkenende III following the resignation of Sybilla Dekker, taking office on 26 September 2006.

Following the end of his active political career, Winsemius again returned to the private sector and the public sector and resumed his previous positions (Vereniging Natuurmonumenten, Energy Research Centre, Stichting Pensioenfonds ABP and the Scientific Council for Government Policy) and as an advocate, lobbyist and activist for Conservation, Environmentalism, Sustainable development and Climate change issues.

Trained as a physics scientist, and active as partner in the business consultancy firm McKinsey, he was Minister of Housing, Spatial Planning and the Environment (VROM) in the First Lubbers cabinet, on behalf of the VVD.