This book is the second volume of The Law and Ethics of Freedom of Thought. The first, published in 2021, explored conceptual questions regarding what a right to freedom of thought does or should protect, the history of that concept, and its implications in the twenty-first century. This volume looks more closely at the challenges raised for liberty and privacy of thought raised by emerging neurotechnologies. In doing so, it analyzes arguments for “cognitive liberty” and how courts defining and applying freedom of thought in international law might understand the right and give it effect. The book addresses key issues related to mental privacy and the challenge of protecting it when the contents of our minds become more objectively manifested through techniques such as neuroimaging. It also explores how questions about the privacy of thought relate to the challenge of more clearly defining the right to freedom of thought: What does the “thought” protected by that right mean more precisely, and does it enjoy a privileged, even absolute protection against the use by governments and private actors of new technologies of “brain reading”?