Step by step the theory was developed. After Abragam and Pound published their work on the theory of PAC in 1953 including extra nuclear fields, many studies with PAC were carried out afterwards. In the 1960s and 1970s, interest in PAC experiments sharply increased, focusing mainly on magnetic and electric fields in crystals into which the probe nuclei were introduced. In the mid-1960s, ion implantation was discovered, providing new opportunities for sample preparation. The rapid electronic development of the 1970s brought significant improvements in signal processing. From the 1980s to the present, PAC has emerged as an important method for the study and characterization of materials, e.g. for the study of semiconductor materials, intermetallic compounds, surfaces and interfaces, and a number of applications have also appeared in biochemistry.