The Molecular Imaging and Contrast Agent Database (MICAD) is an online source of information on in vivo molecular imaging agents based on recommendations from the extramural community. MICAD was established as a key component of the “Molecular Libraries and Imaging” program of the NIH Roadmap, a set of major inter-agency initiatives accelerating medical research. By linking programs in molecular imaging, molecular probes, and molecular libraries, the NIH Roadmap provides much needed support for the development of new, more specific therapies for a wide range of diseases. MICAD is edited by a team of scientific editors and curators at the National Library of Medicine, National Institutes of Health. This program is under the guidance of a trans-NIH panel of experts in the field. The database includes but is not limited to agents developed for positron emission tomography (PET), single photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), ultrasound (US), computed tomography (CT), optical imaging, planar radiogragphy, and planar gamma imaging. It contains textual information, references, numerous links to MEDLINE, and additional related resources at the National Center for Biotechnology Information (NCBI) and elsewhere.