Gender, racial, and ethnic differences occur in vocational and cognitive ability assessments when the average scores of various groups are not equal. Results of such assessments indicate that not all groups are equally represented at all points of the assessment continuum. Many attempts to reduce or minimize existing group differences have been unsuccessful, and current research has failed to account fully for the sources of these differences. This chapter provides a summary of group differences on vocational assessments. The information is intended to provide a broad understanding of the core issues in the assessment process and provide accurate information concerning the magnitude of existing group differences. (Contains 37 references and a table.) (Author)