  In this article we present diverse experiences of Polish mathematicians (in a
broad sense) who during World War I fought for freedom of their homeland or
conducted their research and teaching in difficult wartime circumstances. We
first focus on those affiliated with Polish institutions of higher education:
the existing Universities in Lw\'ow in Krak\'ow and the Lw\'ow Polytechnics
(Austro-Hungarian empire) as well as the reactivated University of Warsaw and
the new Warsaw Polytechnics (the Polish Kingdom, formerly in the Russian
empire). Then we consider the situations of Polish mathematicians in the
Russian empire and other countries. We discuss not only individual fates, but
also organizational efforts of many kinds (teaching at the academic level
outside traditional institutions-- in Society for Scientific Courses in Warsaw
and in Polish University College in Kiev; scientific societies in Krak\'ow,
Lw\'ow, Moscow and Kiev; publishing activities) in order to illustrate the
formation of modern Polish mathematical community.
