The structure of the Main Examination in the UPSC Civil Services Exam consists of nine papers, including mandatory papers and optional subjects. The examination includes a combination of qualifying papers in any Indian language and English, along with several optional papers that are chosen by the candidate from a list of subjects. The written examination assesses comprehensive knowledge, analytical skills, and the ability to articulate thoughts effectively. Following the written part, candidates who qualify are called for the interview stage, ensuring a holistic evaluation of their suitability for civil service.