Major advances have been made in our understanding of autonomic and sensory transmission and function during the past two decades. These include (i) the establishment of the role of sympathetic and parasympathetic ganglia in relaying neuronal information from the central nervous system to effector organs, (ii) the recognition that enteric ganglia, the third component of the autonomic nervous system, contain independent integrative circuits that control complex local activities, (iii) the evidence for local effector functions of primary sensory nerves in addition to their role in sensory transmission, and (iv) the discovery of plasticity of both autonomic and sensory neurons during disease states and inflammation. A major contribution to these new concepts has been the recognition that in both autonomic and sensory ganglia a variety of transmitters coexist in single neurons. Co-transmission is a widespread phenomenon that enables autonomic and sensory neurons to exert fine and highly regulated control of various functions such as circulation, respiration, digestion, and immune response. This chapter will focus on the general principles and specific features of autonomic and sensory ganglia, with a particular emphasis on their general organization and neurochemical properties. Classical concepts and modern principles of classification of autonomic and sensory ganglia are discussed.