The study presents the key concepts of the quality of higher education institutions and quality assurance (i.e. quality improvement and accountability). It describes the broader context of quality assurance efforts including the EAQAHE (European Association for Quality Assurance Agencies in Higher Education). The emphasis is on the integration of internal evaluation (done by the education institution itself) with external evaluation carried out by authorities. The core of the study focuses on the eduational-psychological aspects of external evaluation in the special case of state-wide evaluation using students' assessments of quality. Such evaluation is summative and based on students' long-term experiences with the teaching and learning at a particular department/university (DUE – Departmental and University Experiences). The study considers the influences affecting the validity of such assessments, reviews the findings of foreign studies about variability of evaluations among higher education institutions within a country, and considers possible reasons. Finally, the study discusses the possible users of external evaluation results.