The eligibility criteria for appearing in the UPSC Civil Services Exam include Indian citizenship, age limits, and educational qualifications. Candidates must be between 21 and 32 years of age (with certain relaxations for reserved categories) and must hold a degree from a recognized university. Additionally, they must meet the required physical standards as specified by UPSC. It is essential for aspirants to thoroughly check these criteria and ensure they fulfill them before applying, as ineligibility can lead to disqualification from the examination process.