Teachers' knowledge has been an important research focus for many decades. Although many empirical studies have been carried out regarding content knowledge and pedagogical content knowledge, less attention has been paid to general pedagogical knowledge (GPK). The focus of this study is the exploration of different definitions and dimensions of GPK and how it has been assessed. A systematic literature review was conducted on the EBSCOhost Web following the PRISMA guidelines. The search and evaluation of eligibility criteria resulted in 23 articles. The results show that the definitions of GPK cover three broad areas: student-related, teaching-related and contextual characteristics. However, the scope of GPK in the empirical studies is more narrow, focusing mainly on student-related and teaching-related dimensions. The results also showed that GPK has been assessed through teachers' own perceptions and, recently, by measuring it with tests. These findings are further discussed and a framework for analysing, developing and assessing teachers' GPK in further studies is proposed.