Crowdfunding is a simple but transformative concept. An entrepreneur proposes a business, charitable, or creative project on a crowdfunding website. If convinced, tens, hundreds or even thousands of individuals commit relatively small amounts of capital to support the idea. Taken together, these contributions may be significant enough to turn the idea into a commercial reality. This industry is still in its infancy, but it topped $3 billion in transactions in 2012 and may top $5 billion by the end of this year.