This report describes a master thesis performed at SICS (Swedish Institute of Computer Science) and KTH (The Royal Institute of Technology) in Stockholm.Ajax stands for "Asynchronous JavaScript and XML" and it's not a programming language, but a suite of technologies used to develop web applications with more interactivity than the traditional web pages.Ajax applications can be adapted for mobile and constrained devices. This has been called Mobile Ajax. While the technique is the same, Mobile Ajax generally is considered to be a special case of Ajax, because it deals with problems specific to the mobile market.The purpose of this thesis has been to examine which possibilities and disadvantages has the Mobile Ajax from developers and users perspective. In addition we compare Mobile Ajax with Java Micro Edition (Java ME) and Flash Lite.This has been done through literature studies and development of a databased chat client (MAIM -Mobile Ajax Instant Messenger). The application sends and receives direct messages in real time between differently mobile devices.