Web services substitution is a promising solution that enables process continuity of SOA-based applications associated with composite Web services (WSs). This chapter proposes an approach that assesses the impact of substitution on the composition and selects the best substitute, from a pool of substitutes, in order to reduce potential conflicts due to different ontologies with other peers in this composition, for example. Two types of impact along with their assessment metrics are defined: local (semantic/policy compatibility matching degree) and global (QoS satisfaction degree). This chapter addresses the selection issue as an optimization problem whose main objective is to minimize the efforts to put into resuming the ongoing composition under some temporal constraints. A set of experiments are conducted as a proof of concept and the findings show that our approach provides the necessary means for achieving Web services substitution with minimal disruption time.