Access and refresh tokens are key to modern authentication systems. Access tokens are short-lived and used to access protected resources, while refresh tokens are long-lived and used to obtain new access tokens without re-authentication. This improves both security and user experience by minimizing login prompts and limiting the damage of token leaks. They're ideal for microservices and scalable architectures, supporting granular permissions. Best practices include secure storage (like HTTP-only cookies), token rotation, scope limitation, and monitoring for suspicious activity. Implementing them correctly leads to secure, seamless, and scalable applications.