NRG Energy, Inc. is a large American energy company, dual-headquartered in West Windsor Township, New Jersey, and Houston, Texas. It was formerly the wholesale arm of Xcel Energy, and was spun off in bankruptcy in 2004.

When the state of Texas deregulated the electricity market, the former Houston Lighting & Power (HL&P) was split into several companies. In 2003 HL&P was split into Texas Genco (which got the power plants), CenterPoint Energy (which got the distribution system) and Reliant Energy (which provided the electricity to business and individuals).

In 2006, NRG Energy bought Texas Genco from a group of private equity firms for roughly $5.9 billion. Afterwards, in May 2009, NRG Energy acquired the retail operations of Reliant Energy. With those two moves, NRG's holdings represented most of the former HL&P and today serve 1.6 million customers in Texas. The retail operations continue to operate under the Reliant Energy name while the remainder of the former Reliant Energy became RRI Energy.

Following the acquisition of Reliant, NRG extended its retail footprint with the acquisition of Green Mountain Energy in November 2010. In doing so, NRG also became the largest retailer of green power in the nation, providing all of its Green Mountain and many of its Reliant customers with energy derived from 100% renewable resources.

NRG Energy completed its acquisition of GenOn Energy in December 2012 for $1.7 billion in stock and cash. The GenOn name was retired in the merger, but the combined company retained GenOn's Houston headquarters to coordinate operations.

In August 2013, NRG acquired Energy Curtailment Specialists, a Buffalo, New York based Demand response company. The terms of the deal were not disclosed

In September 2014, NRG acquired Goal Zero, a manufacturer of personal solar power products.

NRG Energy holds the naming rights to the NRG Park campus in Houston, Texas, home to the NRG Astrodome, NRG Stadium, NRG Arena and NRG Center.

On March 12, 2014, NRG Energy announced that they would be re-branding Reliant Park to replace "Reliant" on all signages to "NRG".

After the GenOn merger, NRG has 47,000 MW of total generation capacity, enough to power approximately 40 million homes. Its nearly 100 power plants are located in 18 states in the Northeast, Chicago area, Gulf Coast, Southwest, Nevada, and California. Generation facilities include mostly fossil fuel power plants powered by natural gas, oil, and coal; plus four wind farms (in Texas) and six solar farms (in California, Arizona, and New Mexico). NRG also has a 44% ownership stake in the South Texas Nuclear Generating Station and a 37.5% stake in a coal power plant in Gladstone, Queensland, Australia. Some facilities use cogeneration and the company also owns 28 MW of solar distributed generation.

NRG's Retail Power services provide electricity services to more than 2 million homes and businesses, mostly in Arizona and the Northeast.

Beginning in 2009, NRG began an initiative to become a green energy producer in the United States and started investing money in clean energy projects. They include onshore and offshore wind power, solar thermal energy, photovoltaic, and distributed solar power facilities, and repowering of some of their traditional coal plants with biomass. In late 2010, NRG launched the "EVgo" network, the first completely private public car charging station network for electric power vehicles.

The company signed a two-year agreement beginning in January 2011 to provide 100% renewable energy for the Empire State Building.

Assemblywoman Aravella Simotas has been chair of a coalition to support the utility in their plan to replace its "decades-old, dirty" power plant in Astoria with a newer generator. The company stated its intention in 2012 to replace 31 older oil generators with new gas generators that will increase the megawatts of power while reducing emissions.