In this book the author argues for a groundbreaking perspective that knowledge is inherently interest-relative. This means that what one knows is influenced not just by belief, evidence, and truth, but crucially by the purposes those beliefs serve. Drawing from classical Ny?ya epistemologies, the book asserts that knowledge rationalizes action: if you know something, it is sensible to act on it—and the best way to square this with an anti-sceptical epistemology is to say that knowledge is interest-relative. While versions of this view have been debated, they haven’t gained wide acceptance. The author addresses common objections with a refined formulation and explores how this perspective elucidates the role of knowledge in inquiry, daily life, and the history of thought. Key distinctions include the impact of “long odds” situations on knowledge, the distinctive role knowledge has a starting point for inquiry, and the importance of using non-ideal models in theorising about knowledge. Building on decades of scholarship, the author offers a cohesive theory that integrates and clarifies previous works, demonstrating that not only knowledge but also belief, rational belief, and evidence are interest-relative. This book is essential for those seeking a deeper understanding of the intricate relationship between knowledge and practical interests.