Per Rabbi Shraga Simmons at About.com:
Question: Why do male Chasidic Jews have the long side curls in their hair?
Answer: The Torah says, "You shall not round off the peyos of your head"
(Leviticus 19:27). The word peyos refers to sideburns -- i.e. the hair
in front of the ears that extends to underneath the cheekbone which is
level with the nose (Talmud - Makkot 20a). The Talmud explains that
this law only applies to men, not to women.
Maimonides explains that the prohibition of “rounding” prohibits the
removal of sideburns, by razor, tweezers or any other means. Though it
is permitted to trim the sideburns, even very close to the skin, using
Even though sideburns are enough to satisfy the Torah requirement of
peyos, many Jews grow their peyos long as a way of emphasizing the
commandment (Peyos sounds like pious, right?!), or simply of Jewish
identification. Some will curl their peyos, while others while tuck
them behind their ear. It’s just a matter of individual taste, or
Hair is also a symbol of vanity, a preoccupation of how one looks. The
prohibition against cutting off the peyos reminds a person to
de-emphasize his looks, and instead depend on intellect and good
character. (Rabbi Samson Raphael Hirsch, 19th century Germany)
From a mystical perspective, peyos separate between the front part of
the brain which is used for abstract thought that can be used for
holiness, and the back part of the brain that governs the body.
With blessings from Jerusalem,
Rabbi Shraga Simmons