Every curriculum in traffic or queuing theory presents Engset's formula. Published in 1918 this relatively simple, yet powerful piece of scientific achievement became one of the methodological pillars for the designers of communication networks. His basic model is developed from scratch in an unpublished report in 1915. This book tells the story of a remarkable man -- Tore Olaus Engset (1865-1943). Fully occupied with managerial duties of the Norwegian Telecommunication Authority, his spare time he devoted to developing methods for handling teletraffic. Also, he acted in the theoretical breakthroughs of physics during the first quarter of the twentieth century. A cooperation between Professor A Myskja and the editor of Telektronikk, O Espvik, has resulted in a thorough biography of T O Engset. His most important traffic-theoretical works are translated into English and discussed from the viewpoint of current knowledge.