Practically everyone today own and use a mobile phone, along with numerous credit cards. Paying with cash is getting rarer, and the trend is to pay electronically. Existing mobile payment trials and systems have demonstrated the success of mobile payments. However, they have all been tailored to particular actors and application areas, such as transit tickets or vending machines. This thesis focuses on the design and construction of a generalised mobile payment system able to handle every kind of purchase from a vendor machine purchase to a car sale. It does not matter if the seller’s point of sale is connected to the Internet or not. A working prototype of the mobile payment system was implemented to demonstrate the proof of concept, and to allow testing the premises. The prototype test results show that is it possible to create such a general system by using the latest mobile wireless and security technologies emerging on the market today, and the design shows how it is done in a secure and flexible way.