This chapter explores the different interpretations of tautness in both the Soviet and western literature and summarises the available empirical evidence on the effect of tautness. The approaches to this issue are examined separately and their predictions or interpretations of Soviet planning practice are noted. Excessive plan tautness has been claimed as the root cause of underfulfilment of plans. The chapter summarizes critically the findings and compares them against empirical evidence. The chapter sets out the implications for the further analysis of the Soviet enterprise. The planners may be guessing at the true capacity of the enterprise and hence over-estimate it. The changes in the bonus schemes since 1965 point to the increasing discomfort by which Soviet planners viewed overfulfilment. The analysis of both Keren and Hunter contained the idea that there is an optimum degree of tautness towards which planners are moving either through trial and error or through a bonus system that rewards effort.