Scientific Advertising is a book written by Claude C Hopkins and is cited by many advertising and marketing personalities (such as David Ogilvy, Gary Halbert, and Jay Abraham) as a "must-read" book. The Book contains many principles that are common in all performance-based marketing today, such as the idea of testing and measuring ad effectiveness, writing to one person, understanding and using psychology, basing advertising on sales, eliminating risk, learning what the thousands want to understand what the millions will buy. It is indeed impossible to say one understands advertising without having a thorough grasp on the material in this book. David Ogilvy wrote that "Nobody should be allowed to have anything to do with advertising until he has read this book seven times and The book is widely considered the foundation of direct marketing.