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This special volume celebrates the 20th anniversary of the Journal of Statistical Software (JSS) and is a Festschrift for its founding editor Jan de Leeuw. Jan recently retired from his long-held position as founding chair of the Department of Statistics at the University of California, Los Angeles. The contributions to this special volume look back at some of his research interests and accomplishments during the half-century that he has been active in psychometrics and statistics. In this introduction, the guest editors also reminisce on their own first encounters with Jan, ten years ago. Since that time JSS has solidified its place as a leading journal of computational statistics, a fact that has a lot to do with Jan's stewardship. We include a brief history of JSS.