Strangler pattern

The strangler pattern is a method for removing legacy applications in a controlled and gradual manner. The basic idea is that rather than creating a full replacement system (which is expensive and has high risk of complexity and delays) new systems are introduced in the periphery that will gradually replace more and more of the old core system to eventually make it redundant.

This method adheres to a classic agile principle of taking baby steps but with a clear vision of where to go.

Further reading by Martin Fowler.