Many Orthodox Jewish men have beards because the Torah states (Leviticus 19:27) "....and you shall not destroy the edges of your beard." The Talmud, Tractate Kiddushin 35b, learns from this that the prohibition is to shave with a razor. It is permissible to shave but one should only use an electric razor. Unfortunately, not all electric razors are acceptable (since their mechanism acts as a razor). This is why many are careful and do not shave at all. In addition, there is a Kabbalsitic concept that the hair of the beard should be left uncut as each hair is a form of a conduit to the Heavens. That is why among the Chassidim it is considered the norm to leave the beard untrimmed.
