The document outlines a 5-stage typology of book publishing and discusses key properties at each stage. Stage 1 is traditional print book publishing and selling. Stage 2 sees the advent of online bookselling in addition to traditional methods. Stage 3 marks the tipping point of ebooks and increased importance of online discovery. Stage 4 involves direct marketing, no print books, and collecting user data. Stage 5, just emerging, involves selling books by subscription to reduce customer acquisition costs.