Multiple rounds of job interviews may be used where there are many candidates or the job is particularly challenging or desirable. Earlier rounds may involve fewer staff from the employers and will typically be much shorter and less in-depth. A common initial interview form is the phone interview, a job interview conducted over the telephone. This is especially common when the candidates do not live near the employer and has the advantage of keeping costs low for both sides. Once all candidates have been interviewed, the employer typically selects the most desirable candidate and begins the negotiation of a job offer.