Professor Janusz Sondel (1937–2017), a renowned Polish researcher in Roman law, passed away on 12th of September 2017, at the age of 80 years, while still active in research. Janusz Sondel was born on 30th of April 1937 in Lwów. At the age of 20 he completed his legal education in Kraków. He started his academic career as Wacław Osuchowski`s assistant. He obtained his doctoral degree on the basis of studies of depositum irregulare in 1964. Eight years later he became a habilitated doctor after having published his work on precarium. The Council of the State granted him the title of Professor. During sixty years of his scientific work, Janusz Sondel wrote several books and countless papers. He also wrote the monumental Latin to Polish dictionary for lawyers and historians, as well as the great Dictionary of the history and tradition of the Jagiellonian University in Kraków. This paper briefly presents the major areas of his work.