This chapter outlines the current state of development in robust permanent magnets utilizing 3D assemblies of nano and sub-nano clusters. After introducing this innovative concept, the unique properties of these clusters are compared with those of larger particles and bulk materials, with a primary focus on magnetic properties resulting from electron-spin interactions. The discussion then delves into the magnetic interactions within and between clusters by contrasting the size/diameter of individual clusters and the intercluster distances with three key distances that govern magnetic properties. To address the superparamagnetic behavior of small clusters, the concept of exchange-spring magnets is introduced. This involves locking the reverse spin moment of superparamagnetic clusters through interaction with the surrounding matrix media. A significant portion of the content is dedicated to describing various experimental studies, including sample preparations and property measurements. The preparation of cluster-assembly materials is detailed in separate sections, highlighting both vacuum techniques and organometallic chemical syntheses. These sections are distinctly designed for the production of pure model samples and, respectively, for mass production.