First, check to see if your Kindle is WiFi enabled. If it is connected to the internet, your Whispersync is not turned on. Tap on your menu tab, go to Settings, Device Options, Personalize Your Kindle, then Advanced options. If the Whispersync component in not enabled, tap on it and enable it. If your books are still not syncing, your Whispersync Device Synchronization is most likely disabled on your Amazon account. Sign into your account, click on Manage Your Content and Devices the click Settings. Under Device Synchronization, validate that Whispersync is enabled.