Net Promoter Score (NPS) is perhaps the best known customer loyalty tool around today, based on the entirely sound principle that the more customer promoters you have (i.e., customers who say on surveys that they’re highly likely to refer you to a colleague or friend), the more likely you’ll be to grow your business and outpace the competition. That makes powerful sense, and the continued growth and success of Net Promoter is a testament to the idea’s relevance and value.