In order to identify each level of the European education system, an international classification is usually considered. This classification is called International Standard Classification ISCED 1997 and was carried out by the UNESCO. According to ISCED 1997, the following education levels can be differentiated:

• ISCED 1997 3A-B/4A-B: studies at this level provide students with direct access to tertiary studies, i.e., the following level of the education system. The common terms to refer to this level are Upper Secondary School (ISCED 1997 3) and Post-Secondary Non-Tertiary School (ISCED 1997 4)
• ISCED 1997 5: this level refers to studies at higher education institutions, i.e., at universities and university colleges. Furthermore, ISCED 1997 5 provides access to post-graduate studies (third cycle studies)
• ISCED 1997 6: this level of education refers to post-graduate studies, such as PhD studies (third cycle studies)
• European students’ eligibility for tertiary studies is determined by following their academic achievements at ISCED 1997 3/4. In spite of the large heterogeneity of study contents and structures at upper secondary level across the different education systems, students are guaranteed the fair access to any higher education institution in Europe through the Lisbon Convention. Furthermore, the development of the Bologna Declaration and the use of the ECTS system (European Credit Transfer System) increases the transparency when comparing foreign study courses and programs at ISCED 1997 5, which results in a cohesive European Higher Education Space.