The IAS is a branch of the Indian Civil Services. Aspirants must take the Civil Services Preliminary Exam that is conducted by the UPSC. The Preliminary examination is a screening exam. In 2011, the Preliminary Exam will be held on 12th June 2011.
The Preliminary Exam must be taken by all Indian Administrative Service (IAS), Indian Foreign Service (IFS), Indian Police Service aspirants.
The Civil Services Preliminary Examination pattern was discussed in previous Q&A written of Josh:
The Civil Services Prelimary Examination Syllabus can be found here: https://www.jagranjosh.com/articles/what-is-the-syllabus-for-civil-services-2011-preliminary-examination-1299558504-1
For more details, visit the Jagran Josh Civil Services Center.