This book examines the role of renewable energy certificates in new renewable energy projects. For more than a decade, renewable energy certificates (RECs) have grown in use, becoming a common way to track ownership of the renewable and environmental attributes of renewable electricity generation. RECs are used widely, and are often required, to verify utility compliance with state renewable portfolio standards (RPs) and to substantiate claims made by voluntary purchasers of green power. In recent years, however, questions have risen about the role RECs play in the decision to build new renewable energy projects. Critics point to the uncertain demand for and, in some cases, low prices of RECs as evidence that RECs do not make a meaningful contribution in favour of building a new project. Others counter that any revenue source, large or small, contributes to making new projects profitable and also attracts investment to the broader industry.