With the increasing use of NFC and RFID technology it is important to look at the security, both for the user and for the system owner to see that the system is reliable. NFC is a standard inheriting some of the RFID standards and it is important to see how the old standards have handled security and how it is handled in NFC. There are certain RFID systems that are already in use, which is especially close to NFC. For example is Mifare a system used in many public transportation systems as ticket and in contactless access cards. Another example is electronic passports which uses a standard which is included in NFC. Examining the security in these and also investigate the use of NFC tags to make secure use of them is the focus in this thesis.