The book analyses contemporary relations between two biggest states in East-Central Europe: Poland and Ukraine. This topic is of interest for three reasons: difficult history of the two countries, different models of development adopted after the end of communism and the common challenge of aggressive Russian policy. The timeframe of the work is from 1989-2018, with an emphasis on the period after 2014, when the Russian-Ukrainian war began. The book is divided into three parts. The first part discusses the history and determinants of Polish-Ukrainian relations. The second one presents political, economic, social and military relations between the two states. The last part focuses on more specific issues such as historical memory, the Polish-Ukrainian border and relations with the EU.