The criteria used for the differential diagnosis of well-differentiated thyroid tumors derived from follicular cells are reviewed taking into account the architectural characteristics together with the immunohistochemical and molecular features. The review is focused on follicular carcinoma, papillary carcinoma, follicular variant of papillary carcinoma, and oncocytic (Hürthle cell) tumors, as well as on the recently described borderline lesions: follicular and well-differentiated tumors of uncertain malignant potential, and well-differentiated carcinoma, not otherwise specified.