Currently, the reliance on fossil fuels raises concerns on increasing global energy demand, rapid anthropogenic climate changes and growing environmental problems. The grand challenge is to search for viable carbon-neutral sources of renewable energy. Now nanomaterials are arguably the base that integrates nanotechnology, information technology and biotechnology, the major driver for the technological development of the day. Over the past decades, the understanding of form-function relations surrounding nanomaterials has significantly brightened the prospects of the fossil fuels to solar fuels transition. This book introduces the latest nanomaterials development aimed at the applications in clean energy areas. It is not intended to be exhaustive, but rather to provide a flavor of the close link between nanomaterial development and energy applications from the authors’ own experience and perspective.