This book presents an overview of some trends of research and development in the area of magnetic sensors, from materials to applications. A first focus is made on the topics of amorphous micro-wires and thin-film structures and their fabrication, characterization, and application for magnetic sensors based on the effects of giant magneto-impedance (GMI) and magneto-elasticity. A second section deals with the magneto-impedance (MR) sensors, from the development of new materials to sensor implementation and applications. Intended for readers wishing to acquire understanding of the current trends in these areas and comprehension of the issues and the potential of applications of these sensors, this book addresses exciting topics in this field.