In recent years, assessing (pedagogical) content knowledge has been very popular in vocational education and training (VET) research. Thus, central dimensions of teacher professionality have been studied. Although pedagogical knowledge (PK) represents an important facet of teacher competence, hardly any theoretical or empirical studies related to vocational domains exist. The present paper is dedicated to this desideratum by discussing the relevance of PK in VET from three perspectives. First, from the perspective of VET research, a systematic literature review identifies existing work on PK and analyses the specifics of PK in VET. Second, specific educational principles central and unique to VET education such as the “Lernfeldkonzept” are discussed. Third, a model of PK is presented that combines knowledge theory and domain specifics of VET such as workplace learning. On the basis of that model we suggest further research in order to validly measure PK in VET.