Fred Reichheld's 2006 book The Ultimate Question

That question being, "How likely is it that you would recommend this company to a friend or colleague?" challenged the conventional wisdom of customer satisfaction programs. It coined the terms bad profits and good profits and pointed to a faster, much more accurate way of gauging customers' real loyalty to a company, introducing a quantitative measure (the Net Promoter Score) for establishing a baseline and effectively tracking changes going forward.

Richard Owen and Laura Brooks are co-developers, along with Reichheld, of the methodology behind answering the question. In this book, Owen and Brooks tell how, based on a variety of real case studies, to actually embed Net Promoter discipline in organizations of all types.