Viliam Geffert (born 1955) is a Slovak theoretical computer scientist known for his contributions to the computational complexity theory in sublogarithmic space and to the state complexity of two-way finite automata. He has also developed new in-place sorting algorithms. He is a professor and the head of the computer science department at the P. J. à  afárik University in Koà ¡ice.
Geffert did his undergraduate studies at the P. J. à  afárik University, graduating in 1979. He earned his PhD degree in 1988 from the Comenius University in Bratislava. Since 2003, he is a full professor of the P. J. à  afárik University.