The three stages of the UPSC Civil Services Examination include the Preliminary Examination, the Main Examination, and the Interview (or Personality Test). The Preliminary Exam consists of objective-type questions to screen candidates for the Main Exam, which is more comprehensive and includes descriptive papers. The final stage, the interview, assesses the personality, mental ability, and overall suitability of candidates for a career in civil services. Together, these stages ensure a rigorous selection process to identify suitable candidates for administrative roles in the Indian government.