No area of language assessment research in the past 20 years has received a greater increase in attention than washback research. Beginning with the seminal work of Alderson & Wall (Alderson & Wall 1993; Wall & Alderson 1993), an evolving body of empirical washback studies has been conducted worldwide, especially in countries where English is not the dominant language. A systematic search of the pertinent literature between 1993 and 2013 identified a total of 123 publications consisting of 36 review articles and 87 empirical studies. The focus of this review is on the empirical studies. A further breakdown of these empirical studies reveals 11 books and monographs, 27 doctoral dissertations, 40 journal articles, and 9 book chapters. This intensity of research activity underscores the timeliness and importance of this research topic and highlights its maturity, which in turn calls for this systematic review.