The stages involved in the UPSC Civil Services Examination are: the Preliminary Examination, which consists of objective-type questions; the Mains Examination, which includes written subjective papers; and an Interview or personality test. The Preliminary serves as a screening test, while the Mains evaluates a candidate's depth of knowledge and analytical abilities. Successful candidates from the Mains then proceed to the final Interview stage, which assesses their suitability for a career in civil services.