Change of use is the ability to change the way in which land or buildings are used, either by a simple alteration in the nature of the use, or through alterations and additions which modify the use. A change of use may also arise through a material intensification in the present use, or by subtly altering the present use to a point where the changes amount to development. Certain changes are permissible between and within the use classes without the need for planning permission. Other uses are considered Sui Generis; that is, they are uses on their own unrelated to other uses. A change of use from, say, a field to a caravan park would require planning permission, so too a domestic garage to a business workshop, or house to an hotel etc. You should first consider the permitted development rights then the Use Classes Order to determine whether an intended change of use requires planning permission or not.