My friend and colleagues have released their new book: Software Profit Streams(TM): A Guide to Designing a Sustainably Profitable Business And it has me thinking about what it means to be a sustainable business. My best definition of a sustainable business would be to look at the lifetime longevity of the business . My guess is that a family business would be the most sustainable model. One could include a monarchy in that class of business model (looking at the House of Windsor ).