The interwar Lvov school of mathematics was indubitably a unique phenomenon. In a short space of time it managed to win worldwide recognition although it emerged almost 'ex nihilo' and was not the outcome of an activity pursued by generations of mathematicians but solely of its ingenious founders - Hugo Steinhaus and Stefan Banach. Hugo Dionizy Steinhaus was born on 14 January 1887 in a prosperous Jewish family in Jaslo; here, he graduated from the local secondary school. He studied in Lvov and Ghent, where in 1911 he received his Ph. D. degree. Habilitated in 1917 at the University of Lvov, in 1920 he was offered the chair of mathematics. Stefan Banach was born on 30 March 1892 in Cracow as an illegitimate child of Stefan Greczko, a civil servant, and Katarzyna Banach. He graduated from a secondary school in Cracow and a two-years course at the Lvov Polytechnic (in 1914). In 1920, thanks to Steinhaus' support, Banach was appointed assistant professor at the Polytechnic and in the same year he presented his Ph. D. dissertation at the Jan Kazimierz University in Lvov. The growing scientific rank enjoyed by Steinhaus and Banach (in 1923 Steinhaus was appointed professor ordinary, and Banach was habilitated in 1922; in the same year he became professor extraordinary, and in 1927 - professor ordinary) was accompanied by an expansion of the group of young mathematicians gathered around the two scholars. Next to the considerable scientific accomplishments of the Lvov group attention is due also to the manner of its cooperation. Mathematical discussions were frequently conducted in Lvov cafes and inns while savouring the local dishes and imbibing gallons of coffee and alcoholic beverages (particularly true of Banach and his closest collaborators). In his contacts with the students Steinhaus invariably followed his favourite maxim: 'If you wish to inspire others you must first set the example yourself'. His attitude resembled that of Banach but he tended to implement his convictions in a different mode by teaching order and a systematic approach, always accompanied by a great dose of humour and tolerance. Despite their dissimilar personalities, Stefan Banach and Hugo Steinhaus benefited from close cooperation. They rapidly created a mathematical school of international renown, based on a unique partnership. Not only did the two men possess extraordinary creative skills but they were capable of 'infecting' their students with a passion for mathematics.