Here, we discuss the potential of user interfaces built from NFC phones and NFC tags. We present these NFC-based user interfaces as components of interactive spaces, environments equipped with rich user interfaces and offering a large variety of services for users. Moreover, we specify an interaction model for NFC-based user interfaces and a graphical language for advertising NFC tags. In the model, interaction is decomposed into discovery, composition and usage stages and described using users, tokens, resources, and services. The language provides graphical elements for advertising a large set of different services and commands in a uniform manner. Attention, interaction, technology, and action elements are the most important ones and additional information can be given with context and instruction elements.