Flame spray pyrolysis (FSP) demonstrated enormous potential in the synthesis of single- and multi-element oxide nanoparticles at small laboratory or large industrial production scales. During the course of the past decades, numerous studies proved the applicability of FSP-made nanoparticles in catalysts, gas sensors, energy storage devices, bioimaging, among others, which was recognized by established industries and eventually triggered the foundation of new companies. FSP manages to create such a versatile array of nanoparticle materials because nearly any element from the periodic table can be combined with another by dissolving the desired metal-containing precursor species in a combustible carrier solvent. This liquid mixture is continuously fed into a nozzle, dispersed into a spray of droplets by means of oxygen gas and subsequently ignited by a pilot flame resulting into spray flame that provides the energy to transform the precursor species into metal oxide products which are collected from the downstream gas via filtration or thermophoresis. Despite the past success of FSP, there is a continuing interest in understanding the physical and chemical fundamentals of the reactive multiphase flows that are at the very core of this technology. This book aims to gain deeper insights into the FSP process by employing both experimental diagnostics and numerical methodologies. The work details an extensive state of the art overview and investigates the complex precursor-solvent chemistry, the evolution of metal oxide nanoparticles in open and enclosed FSP reactors as well as the collection of metal oxide aerosol products by means of filtration and thermophoresis.