This volume presents the proceedings of the Second Workshop on Algorithms and Data Structures (WADS '91), held at Carleton University in Ottawa. The workshop was organized by the School of Computer Science at Carleton University. The workshop alternates with the Scandinavian Workshop on Algorithm Theory (SWAT), continuing the tradition of SWAT '88 (LNCS, Vol. 318), WADS '89 (LNCS, Vol. 382), and SWAT '90 (LNCS, Vol. 447). From 107 papers submitted, 37 were selected for presentation at the workshop. In addition, there were 5 invited presentations.