An angel investor or angel (known as a business angel or informal investor in Europe), is an affluent individual who provides capital for a business start-up, usually in exchange for convertible debt or ownership equity. A small but increasing number of angel investors organize themselves into angel groups or angel networks to share research and pool their investment capital.

Source and extent of funding

Angels typically invest their own funds, unlike venture capitalists, who manage the pooled money of others in a professionally-managed fund. Although typically reflecting the investment judgment of an individual, the actual entity that provides the funding may be a trust, business, limited liability company, investment fund, etc.

Angel capital fills the gap in start-up financing between "friends and family" (sometimes humorously called "friends, family, and fools") who provide seed funding, and venture capital. Although it is usually difficult to raise more than a few hundred thousand dollars from friends and family, most traditional venture capital funds are usually not able to consider investments under US$1–2 million. Thus, angel investment is a common second round of financing for high-growth start-ups, and accounts in total for almost as much money invested annually as all venture capital funds combined, but into more than ten times as many companies (US$26 billion vs. $30.69 billion in the US in 2007, into 57,000 companies vs. 3,918 companies).

Of the US companies that received angel funding in 2007, the average capital raised was about US$450,000. Software accounted for the largest share of angel investments, with 27 percent of total angel investments in 2007, followed by healthcare services, and medical devices and equipment (19 percent) and biotech (12 percent). The remaining investments were approximately equally weighted across high-tech sectors. Angel financing, while more readily available than venture financing, is still extremely difficult to raise.

Investment profile

Angel investments bear extremely high risk and are usually subject to dilution from future investment rounds. As such, they require a very high return on investment. Because a large percentage of angel investments are lost completely when early stage companies fail, professional angel investors seek investments that have the potential to return at least 10 or more times their original investment within 5 years, through a defined exit strategy, such as plans for an initial public offering or an acquisition. Current 'best practices' suggest that angels might do better setting their sights even higher, looking for companies that will have at least the potential to provide a 20x-30x return over a five- to seven-year holding period. After taking into account the need to cover failed investments and the multi-year holding time for even the successful ones, however, the actual effective internal rate of return for a typical successful portfolio of angel investments is, in reality, typically as 'low' as 20-30%. While the investor's need for high rates of return on any given investment can thus make angel financing an expensive source of funds, cheaper sources of capital, such as bank financing, are usually not available for most early-stage ventures, which may be too small or young to qualify for traditional loans.