Mechanical, thermal, electronic, optical and magnetic properties of materials are determined by their underlying structure. This knowledge is essential for understanding the world around us and present developments in materials science and nano-technology, such as new nano-electronics, photonic structures, plastic solar cells or superconducting materials. A thorough understanding of materials properties requires special approaches to deal with systems consisting of many interacting particles. Use of periodicity and symmetry of crystal lattices, concepts like ‘reciprocal space’ and quantum mechanical quasi particles play an important role. In this course you will learn how to apply simple models to describe such complex materials in an elegant way.