This paper is the first in a two part work examining how to predict grade-recovery curves. This first part examines some of the theoretical aspects of the method, while the second part shows how the method can be applied to industrial data. The method requires that two relationships be known: the instantaneous grade as a function of the tailings grade and the concentrate mass rate as a function of the tailings grade. The useful feature of these two relationships is that they do not depend on the feed rate or grade, but do depend on the cell operating conditions. These relationships can be used to create both batch flotation and down a bank grade-recovery curves. in the process demonstrating that the batch curve represents the best possible performance for a given operating condition and feed grade. This paper also demonstrates how these curves can be interpreted and used to improve circuit performance. (C) 2008 Elsevier B.V. All rights reserved.