Stepwise refinement is the idea that software is developed by moving through the levels of abstraction, beginning at higher levels and, incrementally refining the software through each level of abstraction, providing more detail at each increment. At higher levels, the software is merely its design models; at lower levels there will be some code; at the lowest level the software has been completely developed.

At the early steps of the refinement process the software engineer does not necessarily know how the software will perform what it needs to do. This is determined at each successive refinement step, as the design and the software is elaborated upon.

Refinement can be seen as the compliment of abstraction. Abstraction is concerned with hiding lower levels of detail; it moves from lower to higher levels. Refinement is the movement from higher levels of detail to lower levels. Both concepts are necessary in developing software.