Tomaž Pisanski (b. May 24, 1949 in Ljubljana, Slovenia) is a Slovenian mathematician working mainly in graph theory. In 1980 he calculated the genus of the Cartesian product of any pair of connected, bipartite, d-valent graphs using a method that was later called the White-Pisanski method. In 1982 Vladimir Batagelj and Pisanski proved that the Cartesian product of a tree and a cycle is Hamiltonian if and only if no degree of the tree exceeds the length of the cycle. They also proposed a conjecture concerning cyclic hamiltonicity of graphs. Their conjecture was proved in 2005 by Dimakopoulos, Palios and Poulakidas.
Pisanski studied at the University of Ljubljana where he obtained a B.Sc., M.Sc and Ph.D. in mathematics. His Ph.D. thesis from topological graph theory was written under the guidance of Torrence Parsons. During his undergraduate studies he was an exchange student at the University of Nancy, France. He also obtained a M.Sc. in computer science from the Pennsylvania State University.
Currently, Pisanski is a professor of discrete and computational mathematics at the University of Ljubljana. Since 2004 he has held a joint position at University of Primorska in Koper. He has taught undergraduate and graduate courses in mathematics and computer science at the University of Zagreb, University of Udine, University of Leoben, California State University, Chico, Simon Fraser University, University of Auckland and Colgate University. From 1998-1999 he was chairman of the Society of Mathematicians, Physicists and Astronomers of Slovenia. In 2005 he was decorated with the Order of Merit (Slovenia).