I have been working as a software consultant for more than 11 years. Because of that I am an eager supporter of lean principles and agile methods.
I have this really great little booklet called The Toyota Way, that I want to recommend. It’s a 60-page summary of the Toyota Production system with the 14 priciples and all the LEAN ideas. It’s summarized from Jeffrey Liker’s book with the same title.
Unfortunately I have only been able to find the summary in Swedish. You can order your own copy for free.