The study of productivity in marketing has received much attention from researchers for many years. Productivity can be defined as the ratio of output to input. However, the definition of what constitutes channel output has been given various interpretations. This has created some confusion in the literature as to the true underlying meaning of channel output. This paper serves to eliminate the confusion by reviewing the literature on channel output. I classify channel output into physical units, sales or dollar value, value added, gross margin and distribution services. For each classification, its advantages and disadvantages are discussed. Major applications in the marketing literature are noted. Suggestions for future research are provided.