In vertebrate and invertebrate systems, the role of glia-neuron interactions during development and behavior is becoming apparent. Recent studies have been aimed at characterizing glial-expressed proteins that affect the modulation of activities traditionally thought to be regulated by the neuron itself. The soil nematode Caenorhabditis elegans has recently emerged as an important invertebrate model to study glial roles in nervous system function and development. My dissertation work focuses on the characterization of HLH-17, a C. elegans basic helix-loop-helix transcription factor that is strongly and constitutively expressed in the glial cells that associate with four of the cephalic (CEP) neurons in the head of the animal. The CEP neurons are four of eight dopaminergic neurons with well characterized roles in the modulation of a number of behavioral activities in the worm. Although HLH-17 is required for neither the specification nor the development of the CEPsh glia or the CEP neurons, it does have a defined role during dopamine responses. We show that HLH-17 functions upstream of the dopamine receptors DOP-1, DOP-3 and the dopamine transporter DAT-1 to affect DA-dependent behaviors. Also, our microarray analyses provide preliminary evidence that HLH-17 targets factors responsible for receiving and transducing signaling molecules that are involved in the modulation of synaptic events in the worm nervous system. Together these results point to a role for HLH-17 in glia-neuron interactions in C. elegans. My dissertation studies therefore provide further support for the role of glial-expressed proteins in the regulation of activities mediated by the nervous system.