A central issue in developmental biology is how a complex organism arises from a single cell. In both plant and animal development, this occurs by a combination of intrinsic information within cells as well as signals transmitted between cells that result in proper patterning of the embryo. Because of the central role of cell communication, intercellular signaling and signal transduction is an important consideration for understanding development as well as the interplay of signaling and transcription. The transcriptional state of the cell depends upon its prior history and the signals it receives. In turn, the signals produced by a cell and its ability to respond to signals are programmed to a large extent by its transcriptional state. The particular wiring of these signals→transcription→signals circuits determines how cells communicate to specify their fates in particular patterns. ; © 2000 Elsevier Science Ltd. Available online 14 July 2000.