This chapter provides an introduction to data matching. It starts with a discussion on the aims and major challenges of data matching. Section 1.2 then describes how data matching fits into the larger process of data integration, data pre-processing and link analysis, and explains the differences between data matching, schema matching and data fusion. Section 1.3 provides a brief history of data matching, starting from the earliest developments of ad hoc matching systems in the health sector and national censuses, all the way to recent developments in collective data matching techniques, and privacy-preserving data matching. With the increasing use of data matching in various application areas, it is worth looking at example applications and exploring the different approaches to data matching that have been developed, as well as to describe the various challenges that occur in different application areas.