Wet chemistry in organic solvents has proven highly efficient for the preparation of several types of metallic, metal-oxide, and semiconductor nanostructures. This chapter reviews the role of oleylamine (OAm) on the synthesis of various types of nanoparticle systems. It is devoted to nanostructures that contain at least one magnetic element (iron, carbon monoxide, nickel, etc.). The chapter discusses noble “nonplasmonic” nanomaterials (e.g. palladium- and platinum-based), while plasmonic nanostructures (gold, silver, copper) are presented. It discusses the use of OAm for the synthesis of semiconductor nanomaterials (for example, sulfur-based systems). The chapter shows some examples the OAm-based synthesis of heterostructures comprising a metal and a metal oxide with combined properties. It presents the preparation of certain kinds of nanostructures containing rare-earth elements and also presents several examples of large-scale nanoparticle synthesis.