There seems to be some confusion regarding what is lean and what is agile software development. Sometimes they are treated as essentially the same and at other times some (agile people) think that lean is just another management fad, while agile is the real stuff. In my definition Lean is a management system, that under a set of principles has as its ultimate purpose to eliminate waste in all processes. For each different business a lean system will look different. For a large number (maybe the majority) of software developing organizations, agile methods, are examples of processes with inherently little waste. So they form a good starting point for a lean organisation. Below that is a set of engineering principles (test early, continuous integration etc), of which many came together in eXtreme Programming, but has been used by good developers and organizations for many years. These are the sound groundwork any lean organization should build upon.
Computerweekly had this interesting article on the topic yesterday.

By Bent Jensen