Given the insufficient involvement of business investments in adult education, this study focused on the factors that motivate managers and entrepreneurs to invest in continuing education. For this purpose, we conducted a systematic literature review of studies referenced in Scopus and Web of Science since 2015. The factors for training were classified into four levels: personal, organizational, industry-related, and national. The results indicated that the inside firm-related determinants are the most studied and essential. A consensus emerged in the relevant literature on the positive impact of a supportive workplace culture, a learning orientation, formalized human resource development practices, and employee voice. The long-term orientation of managers and the perception of employees’ flexibility and adaptability to change also play a role. The study highlights the increasing pressure from regulations and market competition, as well as the (in)capability of universities to provide training tailored to the specific needs of companies. Although institutional factors appeared to predominate, economic considerations also influence training decisions; the latter means that the two underlying theories – institutional theory and human capital theory – complement each other when explaining employers' incentives to invest in training.