The eligibility criteria for appearing in the UPSC Civil Services exam include several factors. Candidates must be Indian citizens, at least 21 years old, and not exceed the age limit, which varies by category (General, OBC, SC/ST). They must hold a bachelor's degree from a recognized university. Additionally, candidates must meet certain physical standards (if applicable) and can attempt the examination a limited number of times depending on their category. It's essential for aspirants to check the official UPSC guidelines, as these criteria may change or require specific documentation.