You know the type: the person everyone turns to with questions, whether it’s which restaurant to go to, where to travel, or how to go about finding a new job. According to Ed Keller and Jon Berry, such people are Influentials, and their brand of peer-to-peer advice isn’t idle chatter, but rather the basis for a national conversation that drives the decision- making of 9 out of 10 Americans.

In their valuable new book, The Influentials (Free Press), Keller and Berry don’t just describe who the influentials are; they also demonstrate how Influentials serve as leading indicators of product-and-service adoption, the spirit of the times, and future trends. Marketers today will do anything for an edge. Here’s a main line to the one conversation that matters.