An amphibious vehicle for land and water use comprises a main mono hull section and a pair of port and starboard sponsons which are movable from a stowed position under a main vehicle deck adjacent to the mono hull and a fully deployed position in which the sponsons are spaced apart from the mono hull by at least one hull width. The sponsons are each pivotally connected to the main hull by means of a pair of respective arms which together with the sponson and the hull define a parallel type four bar linkage. The sponsons stabilise the vehicle on water and are readily stowed to allow vehicle mobility on land.