Information and communication technologies have created exciting new opportunities for teachers, both in the conduct of their professional lives and in the organization and practice of their classroom instruction. But these tools also have opened up new domains of expertise for them to master. Since teachers first began negotiating the single-computer classroom in the early 1980s, CCT has been exploring what teachers would like technology to do for them, the obstacles they encounter when they seek to integrate new technologies into their work, how they learn both about and through new technologies, and how sustained engagement with these tools can, over time, contribute to sustained change in teachers' beliefs and practices.