Clean technology, in short cleantech, is any process, product, or service that reduces negative environmental impacts through significant energy efficiency improvements, the sustainable use of resources, or environmental protection activities. Clean technology includes a broad range of technology related to recycling, renewable energy, information technology, green transportation, electric motors, green chemistry, lighting, grey water, and more. Environmental finance is a method by which new clean technology projects can obtain financing through the generation of carbon credits. A project that is developed with concern for climate change mitigation is also known as a carbon project.

Investments in clean technology have grown considerably since coming into the spotlight around 2000. According to the United Nations Environment Program, wind, solar, and biofuel companies received a record $148 billion in new funding in 2007 as rising oil prices and climate change policies encouraged investment in renewable energy. $50 billion of that funding went to wind power. Overall, investment in clean-energy and energy-efficiency industries rose 60 percent from 2006 to 2007. In 2009, Clean Edge forecasted that the three main clean technology sectors, solar photovoltaics, wind power, and biofuels, would have revenues of $325.1 billion by 2018.