In this paper we outline different ways to make magnetic fluids from colloidal self-assemblies (normal and reverse micelles) and describe the preparation of both ferrite nanocrystals with various compositions and cobalt metal nanocrystals. The general magnetic behaviors are described but it is found that these are not applicable to the whole variety of ferrites produced. Ferrite and cobalt magnetic fluids are organized, in 3D superlattices to form various mesoscopic structures. Within a number of limitations, the magnetic properties of both the above nanocrystals and these fluids have been determined and described.