Superconductors exhibit zero resistance andcomplete diamagnetism below critical temperatures. Since the discovery of thefirst Mercury superconductor, superconductivity has been the central topic incondensed matter physics. In 1986, a new class of materials calledhigh-temperature superconductors (HTS) was discovered. Unlike conventionalmetal or alloy superconductors with low critical temperatures, HTS can achievezero resistance and complete diamagnetism at much higher temperature (e.g. 93 Kfor Y-Ba-Cu-O). Although more than 3 decades has past, the mechanism of HTS isstill a mystery. The understanding of HTS could potentially help us designroom-temperature superconductors and benefit the society.This course lays out the history of theresearch of superconductivity, discuss the basic theory and experimentalprogress in the field, with emphasis in experimental research in unconventionalsuperconductivity.