The sensitivity principle is a compelling idea in epistemology and is typically characterized as a necessary condition for knowledge. This collection of thirteen new essays constitutes a state-of-the-art discussion of this important principle. Some of the essays build on and strengthen sensitivity-based accounts of knowledge and offer novel defences of those accounts. Others present original objections to sensitivity-based accounts (objections that must be taken seriously even by those who defend enhanced versions of sensitivity) and offer comprehensive analysis and discussion of sensitivity's virtues and problems. The resulting collection will stimulate new debate about the sensitivity principle and will be of great interest and value to scholars and advanced students of epistemology.