John Stuart Mill's influential ideas on liberty are articulated in his essay "On Liberty." He advocates for individual freedom and the importance of personal autonomy, arguing that society should only limit individual actions to prevent harm to others. Mill emphasizes the need for free speech and open discourse as essential to human progress and truth-seeking. His principle of harm famously delineates the boundaries of freedom, positing that individuals should be free to act as they wish if their actions do not harm others, shaping modern liberal thought.