Self-directed learning (SDL) has become increasingly important in today's fast-paced and ever-changing society. This paper explores SDL's historical evolution, theoretical foundations, and practical applications, particularly in online environments. SDL is defined as a personal attribute and a process that empowers learners to take the initiative and responsibility for their education. Key models of SDL, including those by Candy, Brockett and Hiemstra, and Grow, provide frameworks for understanding how learners develop self-direction. The role of social context and the importance of lifelong learning are emphasized, especially during significant events like the COVID-19 pandemic, highlighting the necessity for adaptability in education and work. Additionally, the paper discusses how SDL is facilitated in online learning environments, highlighting the need for learners to develop skills in self-regulation, time management, and effective use of resources to succeed.