Despite its apparent simplicity, the soil-dwelling nematode Caenorhabditis elegans has a surprisingly large capacity to learn and remember. Previous characterization of C. elegans genome and neuronal circuit makes this worm an ideal choice for studying behavior and the mechanisms that underlie it. Through careful behavioral and genetic studies, nematodes have been shown to form both short-term and long-term memory in associative and nonassociative training paradigms. Investigations of mechanosensory habituation and context-dependent learning in C. elegans have uncovered important similarities between learning in C. elegans and learning in vertebrates. These results include the discovery of common behavioral features in nonassociative learning between C. elegans and other organisms along with the identification of conserved genes that govern both nonassociative and associative learning. High-throughput studies have identified hundreds of genes implicated in memory and will potentially lead to insights into the fundamental strategies for encoding memory.