This chapter deals with the selection of growth media for the induction of callus and initiation of liquid suspension cultures from plants. Although the first attempts at initiating cultures of plant cells were made by the German botanist G. Haberlandt at the turn of this century, it has only been during the last three decades that rapid developments in plant cell, tissue, and organ culture have occurred. Since extensive work with microbial cultures was by then already underway, the first medium formulations used for plant culture work were inevitably based on experience of microbes. These media contained several distinct classes of compounds: