I don't think that you have to tell your present boss where you are going, but, as wildwood points out, some contracts of employment restrict where you can go. I know because my contract has such restrictions, although the managemant say that they would be flexible in their interpretation of it. The reason for the restriction, in my case, is that they don't want me passing on inside knowledge to the competition. The thing is, though, isn't he going to find out anyway, in which case it would be best to tell him. Either way, good luck in your new job!