This paper explores how citizen ID documents such as national IDs and driver licenses, will ultimately follow the trend toward mobility. Since citizens rely upon IDs for everyday scenarios, most are ready to use smartphones to simplify this aspect of life as well.The result is the ability to use a smartphone to carry a citizen ID via a secure, digital credential called a mobile ID. This paper specifically reviews the infrastructure required to take mobile IDs from concept to reality including new technologies, guiding principles, cross-border interoperability considerations and real use cases.Provided by HID Global, it also outlines solutions the firm has developed for the sector.