Jan Karel Lenstra (born 19 December 1947, in Zaandam) is a Dutch mathematician and operations researcher, known for his work on scheduling algorithms, local search, and the travelling salesman problem.

Lenstra received his Ph.D. from the University of Amsterdam in 1976, advised by Gijsbert de Leve.

After taking positions at the Eindhoven University of Technology (where he became Dean of the Faculty of Mathematics and Computer Science) and the Georgia Institute of Technology, he returned to CWI as its director in 2003.

[5] In 1997, he was awarded the EURO Gold Medal, the highest distinction within Operations Research in Europe.

In 2011, he was made a knight of the Order of the Netherlands Lion,[2] and the CWI organized a symposium in his honor.