Zebrafish is now becoming one of the most useful model organisms in neurobiology. In addition to its general advantageous properties (external fertilization, rapid development, transparency of embryos, etc.), the zebrafish is amenable to various genetic engineering technologies such as transgenesis, mutagenesis, gene knockdown, and transposon-mediated gene transfer. A transgenic approach unraveled two segregated neural circuits originating from ciliated and microvillous sensory neurons in the olfactory epithelium to distinct regions of the olfactory bulb, which likely convey different types of olfactory information (e.g., pheromones and odorants) to the higher olfactory centers. Furthermore, the two basic principles identified in mice, so-called one neuron-one receptor rule and convergence of like axons to target glomeruli, are basically preserved also in the zebrafish, rendering this organism a suitable model vertebrate for studies of the olfactory system. This review summarizes recent advances in our knowledge on genetic, molecular, and cellular mechanisms underlying the development and functional architecture of the olfactory neural circuitry in the zebrafish.