Tracking users across different applications has enabled application providers to offer the vast majority of their applications for free, as it allows them to target advertising. However, tracking has also proven to be an invasion of user privacy. To counter this, operating system developers have restricted access to unique identifiers in their programming interfaces. However, applications can still combine other non-unique device information to create a unique fingerprint. This report examines what sources of information are available for this purpose on Android and iOS, what types of information are available on both operating systems, and which are different.