Understanding the physics of high temperature superconductors remains one of the biggest challenges for the physicists studying interactions of electrons in solids. I will discuss at an introductory level the concepts of the solid state physics and the underlying principles of superconductivity. After that introduction I will review the progress which has been made in the last several years in the study of the high temperature superconducting materials, and will outline open questions which continue to excite people working in that field.