The aim of this chapter is to provide a clear theoretical basis for the ways in which assessment can support learning, to show how the different formulations of the notion of formative assessment proposed over the last 40 years can be encompassed within a broader over-arching framework, and to use that framework to understand research in related areas. Wiener noted that sometimes the effect of the “feedback loop” is to drive the system further in the direction it is already going, such as population growth with plentiful food and no predators or inflationary price/wage spirals in economics. Such feedback is called “positive feedback” because the effect of the feedback and the tendency of the system operate in the same direction. In other situations, the effect of the feedback is to oppose the tendency, restoring stability by returning the system to a steady state, as with population growth when food supply is limited or the familiar room thermostat.