Thomas Kuhn's 1962 book transformed how we understand scientific change. Against the view that science progresses through steady accumulation of facts, Kuhn argued that it advances through revolutionary shifts between 'paradigms'—frameworks that define what questions are worth asking and what counts as an answer. Normal science works within an accepted paradigm, solving puzzles it defines; anomalies accumulate until a new paradigm displaces the old, redefining the field. Famous examples include the shift from Ptolemaic to Copernican astronomy or from Newtonian to Einsteinian physics. Kuhn's concepts—paradigm, normal science, scientific revolution, incommensurability—entered general usage. The book raised troubling questions: if paradigms are incommensurable, is there progress in science or just change? Critics accused Kuhn of relativism; he insisted he believed in scientific progress but defined it differently. The book remains controversial and essential, required reading for anyone interested in how knowledge advances and how communities of researchers validate claims.