The mechanisms and effects of grain refinement in metals are widely contested, with various theories and models being used to explain. In the case of cast zinc and its alloys, there is scarce research published on grain refinement. To preface further research into the grain refinement of zinc alloys and the effect it has on mechanical properties, this paper investigates zinc alloys and their applications, as well as practices and mechanisms of grain refinement in cast metals. Nucleation theory, nucleant additions, the effect of the peritectic reaction, the solute effect (in the areas of constitutional undercooling and growth restriction factor), the edge-to-edge matching model, and the interdependence theory were investigated. As grain refinement is well known to increase the strength of metals without sacrificing ductility, it is worthwhile to research it as a viable method for improving zinc alloys to expand their use. It was found that, to some extent, every major theory of grain refinement lacks in some areas. The involvement of the peritectic reaction in grain refinement isnt well understood, however the edge-to-edge matching model and the interdependence theory show promise in identifying new grain refiners and estimating the final as-cast grain size in metals, respectively.