Immunohistochemistry has been proven to be one of the most important ancillary techniques in understanding early development processes as it allows both a focus on specific, individual cell behaviors as well as an expanded view of tissue architecture, critical to the morphogenesis of complex and integrated organ systems. The zebrafish (Danio rerio) is a well-established model in the area of developmental toxicology and immunohistochemistry methods have been extensively applied to embryos and larvae to ascertain abnormal development resulting from toxic exposure. This chapter outlines the immunohistochemistry methods (conventional and immunofluorescence) optimized for whole-mount zebrafish embryo and larvae, as well as common pitfalls and suggested ways to overcome them.