Caenorhabditis elegans uses olfaction as one of its primary means to sense the quality of its environment throughout its life span. Accordingly, the animal displays experience-dependent plasticity in olfactory sensorimotor responses at different life stages. These various forms of olfactory plasticity include imprinting, adaptation to prolonged odor exposure, conditioning with appetitive or aversive stimuli, and learning to avoid the smells of foods that make it ill. Moreover, a number of these C. elegans olfactory responses are subject to the aging process, as similar responses are in vertebrates. Indeed, the dissection of C. elegans olfactory plasticity has revealed mechanistic underpinnings at molecular, cellular, and circuit levels that show substantial similarities to the mechanisms underlying learning and memory in other animals, including humans.