Calpine Corporation is the largest generator of electricity from natural gas and geothermal resources in the United States,[3] with operations in competitive power markets.

Through wholesale power operations and its retail businesses, Calpine serves customers in 24 states, Canada, and Mexico.

[6] The name "Calpine" is derived from the company's original California location and alpine, a reference to the Zürich home base of Electrowatt.

Calpine's expansion plan was unsupportable in the economic environment formed by the 2000-2001 California energy crisis and the collapse of Enron.

"[14] Later that year, a new executive leadership team, headed by president and CEO Jack Fusco, joined the company.

[citation needed] In 2012, Calpine's power plant fleet generates a record 116 million MWh of electricity.

In 2015, Calpine acquired the electric provider Champion Energy, expanding channels in its core Texas and Northeastern U.S. markets.

[18] In January 2025, Constellation Energy agreed to acquire Calpine for $16.4 billion ($26.6bn including debt) in a cash-and-stock deal.