The advantages and disadvantages of vocational education and training (VET) have been highly debated in recent years: on the one hand VET is criticized for reproducing social inequality by channelling less privileged students into medium-skilled jobs, while keeping them away from higher education. On the other hand, VET is highly praised for generating smooth transitions to the labour market. In addition, vocationally trained workers might have difficulties adapting to new challenges later in their careers. This chapter aims to present an overview on (1) the relevance and forms of VET existing today, (2) theoretical concepts and (3) recent empirical studies in the field of VET, with a particular focus on comparative research. Comparing countries and country-specific institutions of VET within education systems allows to describe functional equivalents of providing and acquiring vocational qualifications, to compare inequality of access to education beyond compulsory schooling, and to evaluate the impact of institutions on transitions from school to work and later working careers.