This paper outlines Siftables, a novel platform that applies technology and methodology from wireless sensor networks to tangible user interfaces in order to yield new possibilities for human-computer interaction. Siftables are compact devices with sensing, graphical display, and wireless communication. They can be physically manipulated as a group to interact with digital information and media. We discuss the unique affordances that a sensor network user interface (SNUI) such as Siftables provides, as well as the resulting directness between the physical interface and the data being manipulated. We conclude with a description of some gestural language primitives that we are currently prototyping with Siftables.