This article describes and discusses some commonly used single-case experimental designs, including reversal and non-reversal designs. The A-B-A-B design is recommended for use when reversal designs can be used and when the patient's treatment phase needs to be maintained. The B-A-B design is used in situations when studying an intervention or treatment which is already in progress. The A-B1-A-B2-A-Bn design is useful when the aim of the researcher is to study the effects of different levels of a specific independent variable. Two types of non-reversal multiple baseline designs are discussed here.