Proliferation of personal computers and workstations that bring computing power to users of all levels has influenced how people prepare documents. Word processors offer numerous functionalities for formatting documents, and in general improving their presentation quality. In Turkey, computers are increasingly being used for document production; but word processors used lack various tools like spelling checkers specific to Turkish. The problem of spelling checking is very interesting in itself, as Turkish, being very different from many languages, presents special challenges and problems. In this thesis, the design and implementation of a spelling checker for Turkish, which can be incorporated into word processing applications, is presented.