The subjects that are compulsory for the UPSC Civil Services Preliminary Examination include General Studies Paper I and General Studies Paper II (CSAT). General Studies Paper I tests candidates on a wide spectrum of topics, including current events, history, geography, and polity. CSAT evaluates quantitative aptitude, comprehension skills, and logical reasoning. These compulsory subjects are designed to assess a candidate’s general knowledge and analytical skills, forming a basis for their eligibility to progress to the Main Examination stage.