Do you mean to leave a current employer? The proper amount of time is usually two weeks. This is to give the employer time to find a replacement for you. Sometimes, an employer will take less... but you have to ask them and let them know at the time you are giving notice that you would like to keep the working relationship open just in case you ever want to return. It is a way of NOT burning a bridge. But by law you are not required to give any... however, do not expect a high recommendation from your past employers when your work history is reviewed for hire if you make it a habit to just "walk out of the job".
