Inequality in adult learning and education (ALE) participation has been reported by previous comparative studies. In doing so, however, most of efforts have been made to understand such patterns of inequality in ALE participation at the micro-level using a conceptual approach based on human capital theory. While the micro-level approach offers an individualistic and economic perspective on learning, macro-level structural conditions play an important role in creating the circumstances faced by individuals. By performing a critical literature review, this paper intends to build conceptual foundations conducive to understand both micro- and macro-level dimensions implicitly and/or explicitly linked to inequality in ALE participation. Specifically, this paper takes a brief look into social origins as a micro-level factor, and takes an in-depth look into social inequality (i.e. education, economic and skill inequality) and institutional settings (i.e. active labour market policies and strictness of employment protection,) as macro-level factors. These conceptual foundations can be used as a conceptual framework for a cross-country empirical analysis of the degree of inequality in ALE participation.