The structure of the UPSC Civil Services Preliminary Examination consists of two objective-type papers: General Studies Paper I and General Studies Paper II (also known as the CSAT). Each paper carries 200 marks and consists of multiple-choice questions. Paper I assesses candidates on subjects such as History, Geography, Polity, Economy, and Environment, while Paper II evaluates basic numeracy, logical reasoning, and comprehension skills. The total duration for each paper is two hours. The performance in the Prelims determines eligibility for the Mains examination, marking it as a critical stage in the selection process.