The capability to change user agent while working is starting to appear in state of the art mobile computing due to the proliferation of different kinds of devices, ranging from personal wireless devices to desktop computers, and to the consequent necessity of migrating working sessions from a device to a more apt one. Research results related to the hand-off at low level are not sufficient to solve the problem at application level. The paper presents a scheme for session hand-off in Web applications which, by exploiting a proxybased architecture, is able to work without interventions on existing code. Categories and Subject Descriptors C.2.4 [Distributed Systems]: Client/server, Distributed applications. General Terms: Algorithms, Performance, Design.