Concorde is a computer code for the traveling salesman problem (TSP) and some related network optimization problems. The code is written in the ANSI C programming language and it is available for academic research use; for other uses, contact bico@isye.gatech.edu for licensing options. Concorde's TSP solver has been used to obtain the optimal solutions to 106 of the 110 TSPLIB instances; the largest having 15,112 cities. The Concorde callable library includes over 700 functions permitting users to create specialized codes for TSP-like problems. All Concorde functions are thread-safe for programming in shared-memory parallel environments; the main TSP solver includes code for running over networks of Unix workstations.