Aimed primarily at experimental chemists, physicists, electronic engineers and material scientists interested in particulate and granular magnetic materials, this textbook is the culmination of more than forty years' research into the subject.The text is divided into two parts. Part One covers the basic physics of magnetism from a relatively low level, including an explanation of some of the unusual terminology in magnetism such as the idea of poles and flux, whose origins are little understood. The complexity of the unit systems in magnetism are also presented. Thereafter a brief review of the principles of domain theory is presented and thermal activation effects and their correct measurement are discussed in some detail. The topic of exchange bias, where an antiferromagnetic material is grown in intimate contact with a ferromagnet, is presented in significant detail, reviewing old theories and numerical models but then focusing on what has become known as the York Model of Exchange Bias, which is now universally accepted as the model that describes the behaviour of exchange bias systems when grown in the form of granular thin films.In Part Two a detailed description of ferrofluids is presented, including a simple method for their preparation and the various engineering applications in vacuum seals, loudspeakers, sink float separation, and the alignment of non-magnetic entities.A description is provided of the phenomenon of magnetic hyperthermia, which is a developing technology with significant potential applications in medicinal therapies. Other applications of magnetic nanoparticles in biomedicine are also presented. An extensive discussion of magnetic information storage in conventional recording systems is described, including the brief history of the development of this technology, whose scale is now enormous, as most of the cloud computing systems in current use are based on hard drive technology.