This book presents Kazimierz Ajdukiewicz's philosophy. Ajdukiewicz was one of the most distinguished and important philosophers of the contemporary Poland. He produced important ideas in logic, epistemology, philosophy of language, and ontology. He influenced Polish analytic philosophy very much. The collection gives a general account of Ajdukiewicz philosophy and it is the only full presentation of his ideas available in Western languages. The volume is of interest for everybody working in analytic philosophy.