This volume is the result of the Third DIMACS Implementation Challenge that was conducted as part of the 1993-1994 Special Year on Parallel Algorithms. The Implementation Challenge was formulated in order to provide a forum for a concerted effort to study effective algorithms for combinatorial problems and to investigate opportunities for massive speedups on parallel computers. The challenge included two problem areas for research study: tree searching algorithms, used in game search and combinatorial optimization, for example, and algorithms for sparse graphs. Participants at sites in the U.S. and Europe undertook projects from November 1993 through October 1994. The workshop was held at DIMACS in November 1994. Participants were encouraged to share test results, to rework their implementations considering feedback at the workshop, and to submit a final report for the proceedings. Nine papers were selected for this volume.