In view of the crucial importance of the bioactivities of N-acylhydrazone derivatives and their corresponding metal complexes, N-acylhydrazones have recently attracted the attention of researchers in the chemical, biological and pharmaceutical fields. This review aims to describe N-acylhydrazone complexes involving transition metal ions such as copper, chromium, manganese, iron, cobalt, nickel and zinc, and to investigate their properties and possible applications, in various domains. It also tries to examine and determine the most promising applications of a number of transition metal complexes incorporating N-acylhydrazones in the areas of biology, medicine, and pharmacology.