Gastrulation involves of a series of coordinated cell movements to organize the germ layers and establish the major body axes of the embryo. One gastrulation movement is epiboly, which involves the thinning and spreading of a multilayered cell sheet. Epiboly plays a prominent role in zebrafish gastrulation and studies of zebrafish epiboly have provided insights into basic cellular properties and mechanisms of morphogenesis that are widely used in animal development. Although considerable progress has been made in identifying molecules that are required for epiboly, we still understand very little about how these factors cooperate to drive the process. Here, we review work on the molecular and cellular basis of zebrafish epiboly in order to identify unifying themes and to highlight some of the current open questions.