The complex process of lung formation is determined by the action of numerous genes that influence cell commitment, differentiation, and proliferation. This review summarizes current knowledge of various factors involved in lung morphogenesis correlating their temporal and spatial expression with their proposed functions at various times during the developmental process. Rapid progress in understanding the pathways involved in lung morphogenesis will likely provide the framework with which to elucidate the mechanisms contributing to lung malformations and the pathogenesis of genetic and acquired lung diseases.