Organic molecules such as tetracene crystallize into solids that can be semiconductors, metals, or even superconductors. Although they were first developed over half a century ago, it is only fairly recently that the considerable promise that organic semiconductors hold as materials for electroncs, display technologies, and solar cells has begun to be realized. Lightweight, flexible, and inexpensive, these materials offer an attractive balance between cost and performance, complemented by versatility, and functionally accomplished by means of molecular design. I will review the physics of organic semiconductors and describe how their electronic and optical properties can be utilized in a variety of applications.