The book is devoted to the theoretical and experimental research of structure, phase transitions, electric and magnetic properties of organic-inorganic multiferroics with an alkylammonium cation and transition metals complexes. The special attention was devoted to analysis of possible magnetoelectric effects in the most prospective representatives of this family of compounds. The main purpose of this book consists in search of the multiferroics with optimal properties for application in the electronic and computer devices. It would be interesting for the scientists and engineers working in the field of electronic material science, nanoelectronics, solid state physics, as well as for teachers, postgraduates and students of relevant physical, technical and natural specialties.