Near Field Communication (NFC) is a technology widely used for security-critical applications like access control or payment systems. Many of these systems rely on the security assumption that the card has to be in close proximity to communicate with the reader. We developed NFCGate, an Android application capable of relaying NFC communication between card and reader using two rooted but otherwise unmodified Android phones. This enables us to increase the distance between card and reader, eavesdrop on, and even modify the exchanged data. The application should work for any system built on top of ISO 14443-3 that is not hardened against relay attacks, and was successfully tested with a popular contactless card payment system and an electronic passport document.