This chapter outlines travel-based activities with potential for ICT-based substitution, summarizes the results of empirical studies, and reflects on the potential contribution to sustainable transport policy and planning. It aims to give a nuanced examination of substitution effects by detailing the circumstances in which the substitution potential of ICT is and is not triggered. Activities for which the empirical evidence leans towards substitution effects are commuting to work and school, telemedicine, telebanking, and several other services. Common to these activities are that they are often done of necessity, and not for pleasure. Some studies have also illustrated how telecommuting makes room for increased cycling and active travel. But care should be taken when applying policies that encourage ICT-based substitution as there are also circumstances and activities when ICT risks generating additional travel, such as shopping and leisure trips.