Getting Cozy with Drupal Commerce
A developers guide book on Drupal Commerce to be published on LeanPub - https://leanpub.com/getting-cozy-with-drupal-commerce. Being written on GitHub so it can be freely available to the community with optional purchase (for PDF, mobile support.)
This book only exists because of the amazing work done by all of the open source contributors who helped build and continue to grow the Commerce module and its ecosystem.