Adult learning remains an important component of educational systems in countries all over the world, particularly because it seeks to explain how adults obtain education through formal, non-formal and informal modes. While many education providers and researchers focus on increasing resource support and the development of the knowledge and skills of adult learners, there is a paucity of studies on theoretical perspectives that define adult learners for the provision of effective and inclusive adult education. To bridge this gap, this article discusses the characteristics of adult learners based on five major theoretical frameworks -- human capital, adult development, sociocultural, biographical and political perspectives -- and shows how they can enhance effective and inclusive adult education policies and practices at different levels of governance. The author considers these perspectives along with the normative and ontological dimensions of lifelong learning. While the normative dimension explains lifelong learning as a concept that focuses on the development of educational policies, the ontological dimension explains how individuals learn throughout their lives within and outside of educational settings. The study concludes that if policymakers reflect on the five theoretical perspectives, and consider the normative and ontological dimensions, they can enhance the policies and practices that guide adult learners in lifelong learning environments and promote inclusive education, leaving no one behind.