The methods and procedures of evaluation research using single-system or small-N designs are defined and described. Various components of single-system evaluation research, including specifying the problem, measuring and recording the data, selecting an appropriate design, and analyzing the data, are presented and discussed. The argument is made that single-system evaluation research methods are ideally suited to document clinical change on an individual basis and can provide a mechanism for establishing therapeutic accountability. The relationship between single-system evaluation research and the more traditional experimental procedures is briefly explored, and the implications for establishing an empirically derived basis for clinical practice are discussed.