Designing user interfaces for ubiquitous computing applications is a challenging task. In this chapter we discuss how to build intelligent interfaces. The foundations are usability criteria that are valid for all computer products. There are a number of established methods for the design process that can help to meet these goals. In particular participatory and iterative so-called human centered approaches are important for interfaces in ubiquitous computing. The question on how to make interfaces more intelligent is not trivial and there are multiple approaches to enhance either the intelligence of the system or that of the user. Novel interface approaches follow the idea of embodied interaction and put particular emphasis on the situated use of a system and the mental models humans develop in their real-world environment.