This talk concerns a series of efforts in designing, fabricating, and using microfluidic chips to study behavioral neuroscience in a free-living soil nematode – C. elegans. Behavioral neurogeneticists are interested in understanding how genes, neurons, and neuronal connectivity give rise to behavior of an organism. Conventional methods for behavioral neuroscience for small organisms (e.g. C. elegans adults -- 50 microns in diameter and 1 mm in length) do not have the precision and control for delivering stimuli and manipulating individual animals; therefore, these methods have limited use in quantitative analysis of behavior and the neural basis of behavior. By comparison, our microfluidic approach takes advantage of transport phenomena at the micro scale to deliver gas stimuli, control microenvironment, and carry out quantitative behavioral analysis. For example, we can form gas gradient (oxygen or volatile odors) in less than a minute, and maintain a stable gradient for hours to allow behavioral assessment of a population of animals. Moreover, we can also deliver stimuli with accurate and high spatial and temporal resolutions that allow more detailed and quantitative studies of individual animals' behavior. Using these bioMEMS device, we begin to understand details of genetic pathways and neural circuits in olfaction behavior, in particular oxygen sensation/aerotaxis, social behavior, and pathogenic learning in C. elegans. We show that bioMEMS and microfluidic devices have opened a new route to study neuroscience.