In-app purchasing is a common and important way for monetizing apps. This course introduces you to integrating Google Play In-app Billing into Android apps in a comprehensive way. You can get the introduction of the whole image of In-app Billing, learn how the purchase flow works, purchase and consume in-app products, and test In-app Billing in a sandbox. The possible security issues are discussed and suggestions are given on how to deal with the problems. Finally, you will get inspiration on how to increase sales with In-app Billing.