Similar to other animal species, fishes efficiently use the sense of smell for locating food, detecting danger, communicating social information, and memorizing beneficial and detrimental conditions. This review summarizes recent advances in our knowledge of the olfactory system in the zebrafish (Danio rerio), which has become one of the most useful and important model organisms in neurobiology. Olfactory receptors belonging to the OR, V1R, V2R, and TAAR families are differentially expressed in three types of the olfactory sensory neurons (ciliated, microvillus, and crypt) in the olfactory epithelium. In the olfactory bulb, nine glomerular clusters are clearly delineated by anatomical features and molecular markers, serving as functional units important for odor information categorization, coding, and processing. Individual output neurons of the olfactory bulb project axons to a combination of four major target regions in the forebrain: the posterior zone of dorsal telencephalon, the ventral nucleus of ventral telencephalon, the posterior tuberculum, and the right habenula. Distinct modes of odor information decoding are employed by the individual olfactory centers: either nonselective or biased as well as either diffuse or convergent, which contribute to eliciting different physiological and behavioral responses. By taking advantage of its small brain, transparency of larvae, and amenability to various genetic and imaging techniques, zebrafish will pave the way toward understanding the functional organization of the olfactory system as a whole.