Stoicism is an ancient Greek philosophy that teaches the development of self-control, resilience, and virtue as a means to achieve a tranquil and contented life. It emphasizes the importance of accepting what we cannot change, focusing on our own actions and reactions, and cultivating an attitude of rational detachment from external circumstances. Key figures include philosophers like Epictetus, Seneca, and Marcus Aurelius, who advocated for inner peace through the mastery of emotions and the pursuit of wisdom. Ultimately, Stoicism encourages individuals to live in harmony with nature and reason.