A thesaurus of terms is a useful tool for the search and retrieval of data. It helps the user to choose the most suitable terms and to use those terms consistently. KOSSDA Thesaurus has been developed specifically for and by KOSSDA incorporating several reliable sources: the Social Sciences Thesaurus of National Assembly Library of Korea, the HASSET(Humanities and Social Science Electronic Thesaurus) of the UK Data Archive, and the UNESCO Thesaurus.