In psychological and special education research, group comparison experimental designs are more often used than single subject experimental designs. However, the application of group designs poses many difficulties, such as the collection of large numbers of homogeneous subjects for a particular experimental condition, the averaging of individual subjects, and the use of statistical significance tests. In the development of behavior analysis since the 1960's, new experimental design alternatives have appeared which emphasize direct measurement of treatment effects and causal analysis between independent variables and dependent variables. This paper describes single subject experimental designs and discusses general issues in their use. (JDD)