Innovations in technology, along with the growing prevalence of the Internet and its increasing availability in classrooms and homes throughout the world, have created a new class of manipulatives, virtual manipulatives. These "virtual manipulatives" offer a new, enhanced approach for teaching and learning mathematics using manipulatives and computers, one that combines the useful properties of existing computer manipulative programs while overcoming many of their disadvantages. Yet very little is known or written about them. The purpose of this paper is to establish a working definition of virtual manipulatives and discuss unique properties that make them particularly useful for the K-12 classroom. (Author)