Decomposition is a widely used tool to explain a change or difference in an aggregate index by the underlying changes or differences in its parameters. In this chapter we first describe the main developments in the general field of decomposition analysis. Next we turn our attention to the particular case of healthy life expectancy, which is decomposable using the step-wise and continuous change decomposition methods. We describe both methods in detail. Finally, using the R-package DemoDecomp, we demonstrate how to decompose gaps in prevalence-based healthy life expectancy, using either of these two decomposition methods.