Smart objects can be smart because of the information and communication technology that is added to human-made artifacts. It is not, however, the technology itself that makes them smart but rather the way in which the technology is integrated, and their smartness surfaces through how people are able to interact with these objects. Hence, the key challenge for making smart objects successful is to design usable and useful interactions with them. We list five features that can contribute to the smartness of an object, and we discuss how smart objects can help resolve the simplicity-featurism paradox. We conclude by introducing the three articles in this special issue, which dive into various aspects of smart object interaction: augmenting objects with projection, service-oriented interaction with smart objects via a mobile portal, and an analysis of input-output relations in interaction with tangible smart objects.