This volume reprints my publications on matched sampling, or more succinctly, matching, produced during a period of over three decades. My work on matching began just after I graduated college in 1965 and has continued to the present, and beyond, in the sense that there are publications on matching subsequent to those collected here, and I have continuing work in progress on the topic. For most of the years during this period, I believe I was one of the few statistical researchers publishing in this area, and therefore this collection is, I hope, both interesting and historically relevant. In the introduction to each part, I attempt to set the stage for the particular articles in that part. When read together, the part introductions provide a useful overview of developments in matched sampling. In contrast to the earlier years, in the last few years, there have been many other researchers making important contributions to matching. Among these, ones by technically adroit economists and other social scientists are particularly notable, for example: Hahn (1998); Dehejia and Wahba (1999); Lechner (2002); Hansen (2004); Hill, Reiter, and Zanutto (2004); Hirano, Imbens, and Ridder (2004); Imbens (2004); Zhao (2004); Abadie and Imbens (2005); and Diamond and Sekon (2005). Some of these have had a direct or indirect connection to a course on causal inference I've taught at Harvard for over a decade, sometimes jointly with Guido Imbens.