People today commonly have multiple information devices, including smartphones, tablets, computers, home media centers, and other devices. As people have many devices, situations and workflows where several devices are combined and used together to accomplish a task have become usual. Groups of co-located persons may also join their information devices together for collaborative activities and experiences. While these developments towards computing with multiple devices offer many opportunities, they also create a need for interfaces and applications that support using multiple devices together.<br /><br />The overall goal of this doctoral thesis is to create new scientific knowledge to inform the design of future interfaces, applications, and technologies that better support multi-device use. The thesis belongs to the field of Human-Computer Interaction (HCI) research. It contains five empirical studies with a total of 110 participants. The study results have been reported in five original publications. The thesis generally follows the design science research methodology.<br /><br />More specifically, this thesis addresses three research questions related to multidevice use. The first question investigates how people actually use multiple information devices together in their daily lives. The results provide a rich picture of everyday multi-device use, including the most common devices and their characteristic practices of use, a categorization of patterns of multi-device use, and an analysis of the process of determining which devices to use. The second question examines the factors that influence the user experience of multi-device interaction methods. The results suggest a set of experiential factors that should be considered when designing methods for multi-device interaction. The set of factors is based on comparative studies of alternative methods for two common tasks in multi-device interaction: device binding and cross-display object movement. The third question explores a more futuristic topic of multi-device interaction methods for wearable devices, focusing on the two most popular categories of wearable devices today: smartwatches and smartglasses. The results present a categorization of actions that people would naturally do to initiate interactions between their wearable devices based on elicitation studies with groups of participants.<br /><br />The results of this thesis advance the scientific knowledge of multi-device use in the domain of human-computer interaction research. The results can be applied in the design of novel interfaces, applications, and technologies that involve the use of multiple information devices.