Since the publication of the first edition of "Understanding Academic Freedom," the never-ending struggle to defend academic freedom has entered a demonstrably new phase. Legislation determining what can and cannot be taught in schools in Florida, Texas, and other states has intensified governing board activism that impinges on widely accepted faculty prerogatives. Major donors in research, teaching, and institutional governance have grown bold in their interference. Highly polarizing controversies over antisemitism and the Israeli-Palestinian conflict, as well as debates over diversity, equity, and inclusion policies, continue to broil. Taken as a whole, these developments indicate that we have entered a new period in the history of American academic freedom. Academic freedom, long heralded as a core value of American higher education, may now be in as much danger as at any time since the 1950s. But what is "academic freedom"? Is it the right of faculty members to teach whatever they wish; a value upheld for supporters, but not opponents, amid polarizing controversy; or a narrow claim of privilege by a professorial elite, immune from public accountability? Henry Reichman, who chaired the American Association of University Professors' Committee A on Academic Freedom and Tenure for nearly a decade, mounts a rigorous defense of academic freedom and its principal means of protection: the system of academic tenure. Probing academic freedom's role in multiple contexts, Reichman draws on a wealth of historical and contemporary examples to offer a comprehensive introduction to the concept in all its manifestations. This second edition addresses the most recent and pressing issues in academic freedom, making it an indispensable resource for understanding the current controversial climate.