Book is an Android app developed by SoftBank Corp. (東京都港区東新橋1-9-1 東京汐留ビルディング). Others apps created by SoftBank Corp. are: QR.

Book first became available on 10 Mar 2012. It is estimated that Book has been downloaded between 1000000 and 5000000 times from the Play Store.

Book 2.0.1 requires the following permissions:

Allows applications to open network sockets.

Allows an application to read from external storage.

Allows read only access to phone state, including the phone number of the device, current cellular network information, the status of any ongoing calls, and a list of any PhoneAccounts registered on the device.

Allows an application to write to external storage.