This chapter presents the concept and mechanism of venture capital, a key source of finance for new and high-growth ventures. It provides the typical processes of venture capital investments, and defines what an environmental or cleantech venture is, giving an overview of some of the patterns of venture capitalists (VCs) investment into environmental ventures in North America between 1999 and 2006. Since 2004, investments in such cleantech ventures by venture capitalists has hit the mainstream, so much so that it is now regularly described as the third largest venture investing category behind software and biotechnology. The US National Venture Capital Association (NVCA) estimates that some 40 per cent of venture-backed companies in the United States fail; 40 per cent return moderate amounts of capital; and 20 per cent produce high returns. Case-work and interviews reveal to the story of venture capital and the environment than just the types and numbers of deals made in cleantech or environmental technologies.