During 1927-1931 Leśniewski published a series of articles (169 pages) entitled 'O podstawach matematyki' [On the Foundations of Mathematics] in the journal Przeglad Filozoficzny [Philosophical Review], and an abridged English translation of this series is presented here. With the exception of this work, all of Leśniewski's publications appearing after the first World War were written in German, and hence accessible to scholars and logicians in the West. This work, however, since written in Polish, has heretofore not been accessible to most (...) Western readers, and it is hoped that this translation will encourage both the study of Leśniewski's works as well as the further development of his theories. (shrink)