Magnetism and magnetic phenomena surround us. Magnetic materials pervade our lives far beyond just compasses and common household magnets. Magnetic materials and magnetism are used inconspicuously in many complex gadgets, ranging from magnetic recording disks and cellular phones, to magnetic resonance imaging instruments and spintronic devices. Understanding magnetic phenomena and developing new functional magnetic materials pose a big challenge, but also great opportunities, to our scientists and engineers. New characterization techniques help us to understand the fascinating behavior of newly discovered magnetic materials, while new materials stimulate the further development of novel methods. We understand the physical and chemical behaviors of materials through directly or indirectly measuring a material's structure and properties. The field of structural characterization is often too wide; identifLing the most appropriate method to employ can be difficult. One objective of this book is to introduce the reader to various modem techniques in characterizing magnetic materials at different length scales, focusing on neutron, x-ray, electron, and laser-light scattering as well as proximal probes, their principles, applicability, limitations, and relationship to competing methods.