This project explores the creation and use of a physical/digital construction kit. Triangles is a physical computer interface in the form of a construction kit of identical, flat, plastic triangles. The triangles connect together both physically and digitally with magnetic, conducting connectors. When the pieces contact one another, specific connections can trigger specific digital events, allowing a simple but powerful means of physically interacting with digital information. Users can create both two- and three- dimensional patterns whose exact configuration is known to the computer. Triangles is a flexible system in that it can be reconfigured at hardware and software levels for a variety of uses. It is versatile, with applications from storytelling and education to rapid prototyping of human-computer interfaces.