The logic and advantages of unobtrusive measures are briefly reviewed. The literature on unobtrusive measures is then summarized under four large classes-physical traces, archives, simple observations, and measures gathered with hardware. A small number of methods also fall into a residual category.Each class of methods is discussed briefly and recommendations and/or problems with its use are discussed. This is followed by a listing of the measures in that category, an indication of what variable is being indexed and applicable references. he purpose of this paper is not to tout the merits of unobtrusive measures; they are as a rule inferentially weak. The intent is to illustrate a wide variety of them and, by example, to persuade the reader to consider seriously supplementing more traditional procedures with them. Neither will we discuss in any detail the problems entailed by their use. Every user should read the superb methodological discussion in Webb et al. (1966). Other excellent methodological discussions can be found in Brandt (1972, ch. 5) and Denzin (1970, chs. 1 1 and 12).