Magnetism is a science with more than two millennia of recorded history. The attraction of ferrous objects to a permanent magnet across a distance has been a source of curiosity since the iron age. Investigations of magnetic phenomena led to the invention of steel magnets-needles and horseshoes-and the compass that enabled the exploration of the planet. A host of discoveries following Oersted's 1821 demonstration of the relation between electric current and magnetic field led to the electromagnetic revolution that by the end of the 19 th century had resulting in global communications and electrification. The discovery of the electron, together with the emergence of quantum theory and relativity in the early 20 th century established the modern theoretical understanding of magnetism. A panoply of hard and soft magnetic materials has been developed to underpin the modern magnetics industry and a marriage of magnetism and electronics in thin film devices has eased the birth of the information revolution. Aside from the revolutionary technological advances, magnetism played a key role in clarifying basic concepts in condensed matter physics throughout the 20 th century.