INTRODUCTION Even though plants meet most of their energy needs through photosynthesis, a number of vital processes require that the glycolytic and respiratory pathways be operational. During periods of darkness, such as at night or underground in the germinating seed, glycolysis, respiration, the pentose phosphate pathway, and the glyoxylate cycle provide the only means for producing the energy and metabolic intermediates used in biosynthetic reactions. This chapter discusses the enzymology, bioenergetics, and regulation of these metabolic pathways.