A Fortune 500 company based in Houston, Texas, the company is owned by an affiliate of Energy Capital Partners and a consortium of other investors, including the Sullivan Family of San Antonio, Access Industries Inc. and Canada Pension Plan Investment Board. 
Its fleet of 79 power plants in operation represents more than 26,000 megawatts of generation capacity. 
In 2018, while M.J. Bradley & Associates ranked Calpine as the nation’s 10th largest power producer, it ranked the company 75th with regard to emissions of SO2 and NOx and 85th for CO2 with no mercury emissions in its gas-fired fleet.  These results reflect efficient operation of a modern fleet with no coal-fired generation.
Calpine’s predominantly gas-fired fleet also benefits from the nations’ abundant and affordable supply of natural gas and the increasing need for dispatchable power plants to successfully integrate intermittent renewables into the grid. The company advocates for responsible environmental regulation, competitive wholesale power markets and market-driven solutions that result in nondiscriminatory forward price signals for investors.
As of March 2018, the directors of Calpine are CEO Thad Hill; Executive Vice Chairman Thad Miller; Tyler Reeder, Douglas Kimmelman, Andrew Singer and Andrew Gilbert of Energy Capital Partners; and Donald Wagner of Access Industries, Inc. The executive leadership team includes President/CEO Thad Hill, EVP/Chief Legal Officer Thad Miller, EVP/Chief Financial Officer Zamir Rauf, EVP/Power Operations Charlie Gates and EVPs of Commercial Operations Andrew Novotny and Caleb Stephenson.
In response to the 1973 oil crisis and the 1979 energy crisis, much legislation was passed that made domestic energy production an attractive enterprise. In 1984, Peter Cartwright and four of his co-workers, the Guy F. Atkinson Construction Company of South San Francisco, and the Electrowatt corporation struck an investment arrangement, and Calpine was born with initial capital of US$1 million. It was essentially a Silicon Valley startup company. The name "Calpine" is derived from the company's original California location and alpine, a reference to the Zürich home base of Electrowatt. Calpine is the largest generator of electricity from natural gas and geothermal resources in the United States.
- 1984: provider of management services for independent energy companies
- 1988: first power production
- 1992: assets of US $21 billion
- 1994: 141 MW capacity
- 1996: largest IPO ever for an independent energy company
- 1998: purchased 45 gas turbine power plants
- 1999: purchased 18 gas turbine power plants
- 1999: acquired PG&E's plants at The Geysers, making Calpine the world's largest geothermal provider
- 2001: the California electricity crisis
- 2004: Investment bank Lehman Brothers begins shorting Calpine, with researcher Christine Daley lacking confidence in the Calpine. This information spreads to clients of Lehman. By the time Calpine goes bankrupt in 2005, Lehman will profit roughly $100,000,000 from the short.
- 2005: November: CEO Peter Cartwright and CFO Bob Kelly leave the company.
- 2005: December 20: Calpine files bankruptcy, US$22 billion in debt. Calpine's aggressive leveraged expansion plan was unsupportable in the economic environment formed by the 2000-2001 California energy crisis and the collapse of Enron. Stock price dropped to less than US$0.30 per share. Delisted from NYSE.
- 2008: On 1/31/08, Calpine emerges from bankruptcy. Previous stock was exchanged for warrants. New Calpine stock began trading on the NYSE under the ticker symbol "CPN."
- 2008: Executive leadership team headed by President and CEO Jack Fusco join the company.
- 2009: Moved corporate headquarters from San Jose, California to Houston, Texas.
- 2010: Acquired Conectiv Energy (generation) from Pepco Holdings
- 2010: Calpine dedicates the Geothermal Visitor Center and celebrates 50 years of geothermal power production at The Geysers in Northern California.
- 2010: Thad Hill is named Chief Operating Officer.
- 2012: Calpine’s power plant fleet generates a record 116 million MWh of electricity.
- 2013: Calpine rings the opening bell at the New York Stock Exchange on January 18.
- 2014: Jack Fusco becomes Calpine’s Executive Chairman of the Board and Thad Hill becomes the company’s Chief Executive Officer effective May 21.
- 2014: Calpine executes on a strategic priority by selling six power plants in its Southeast region.
- 2015: Calpine acquired award-winning retail electric provider Champion Energy, expanding customer channels in its core Texas and Northeastern U.S. markets.
- 2016: Calpine acquired Granite Ridge Energy Center in Londonderry, New Hampshire.
- 2016: Frank Cassidy becomes Chairman of the Board.
- 2016: Calpine acquires Noble Group Ltd's North American energy business. 
- 2018: Calpine is acquired by an affiliate of Energy Capital Partners and a consortium of other investors, including Access Industries Inc. and Canada Pension Plan Investment Board, on March 8. A new board is named. Shares of Calpine's common stock stop trading prior to the March 9, 2018, opening of the New York Stock Exchange . 
- Don Weinland in Hong Kong and David Sheppard and Neil Hume in London (2016-10-10). "Noble Group sells US energy business in turnround drive".
Calpine Corporation is the largest generator of electricity from natural gas and geothermal in the US.
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- Calpine Corporate press releases, http://investor.calpine.com/investor-relations/news-releases/default.aspx. Multiple dates. Retrieved October 28, 2016.
- http://www.calpine.com/operations/power-operations/our-fleet Retrieved August 9, 2018
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- A Colossal Failure of Common Sense, Lawrence G McDonald, Patrick Robinson, Crown (Random House), 2009, p99-p105, 154
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- "Calpine, Form 8-K, Current Report, Filing Date Apr 21, 2010" (PDF). secdatabase.com. Retrieved Mar 19, 2013.
- Editors, Scientific American (2004). The 2004 Scientific American 50 Award: Business Leaders. Retrieved February 7, 2006.
- Editors, World-Generation. Peter Cartwright. Retrieved February 10, 2006.
- Peters, Sara (2002). Calpine CEO shares wisdom, insight. Retrieved February 10, 2006.
- "Calpine to Trim Jobs, Shed Businesses to Reduce Costs". Los Angeles Times. 2 Feb 2006.
- Schlager, Neil (2006). Peter Cartwright, 1930-. Retrieved February 10, 2006.
- Green, Sherri (2016). http://www.calpine.com/. Reviewed March 8, 2018.