This atlas is the offspring of the “The National Cancer Institute (NCI) Thyroid Fine Needle Aspiration (FNA) State of the Science Conference,” hosted by the NCI and organized by Dr. Andrea Abati. Preparations for the conference began 18 months earlier with the designation of a steering committee and the establishment of a dedicated, p- manent web site. The meeting took place on October 22 and 23, 2007 in Bethesda, Maryland and was co-moderated by Susan J. Mandel and Edmund S. Cibas. The discussions and conclusions regarding terminology and morphologic criteria 1, 2 from the meeting were summarized in publications by Baloch et al. and form the framework for this atlas. The atlas is organized by the general categories of “Nondiagnostic,” “Benign,” “Follicular Neoplasm/Suspicious for a Follicular Neoplasm”, “Suspicious for Malignancy,” and “Malignant,” and it includes the defi- tions and morphologic criteria of these categories as set forth by Baloch et al. The majority of the conference participants also agreed on a category of “undetermined significance,” which is incorporated in this atlas (Chap. 4). It is critical that the cytopathologist communicate thyroid FNA interpretations to the referring physician in terms that are succinct, unambiguous, and helpful clinically. We recognize that the terminology used here is a flexible framework that can be modified by individual laboratories to meet the needs of their providers and the patients they serve.