Abstract. In this paper we extend one of the main tools used in veri cation of discrete systems, namely Binary Decision Diagrams (BDD), to treat probabilistic transition systems. We show how probabilistic vectors and matrices can be represented canonically and succinctly using probabilistic trees and graphs, and how simulation of large-scale probabilistic systems can be performed. We consider this work as an important contribution of the veri cation community to numerous domains which need to manipulate very large matrices.