As Wikipedia approves, there's a difference between Shia and Sunni belief about divorce:
Shia and Sunni Muslims have different rules for performing an Islamic
divorce. Sunni practice requires no witnesses, and allows a husband to
end a relationship by saying the one, two or triple talaq. Shi'a
scholars view the triple talaq (in one sitting or at one time) as a
pagan pre-Islamic custom, forbidden by Muhammad, but reinstated by
Umar ibn al-Khattab, and thus sinful (haraam).
These two verses of Surat at-Talaq have clarified the issue very well:
O Prophet, when you [Muslims] divorce women, divorce them for [the
commencement of] their waiting period and keep count of the waiting
period, and fear Allah , your Lord. Do not turn them out of their
[husbands'] houses, nor should they [themselves] leave [during that
period] unless they are committing a clear immorality. And those are
the limits [set by] Allah . And whoever transgresses the limits of
Allah has certainly wronged himself. You know not; perhaps Allah will
bring about after that a [different] matter.
[At-Talaq: 1]
And when they have [nearly] fulfilled their term, either retain them
according to acceptable terms or part with them according to
acceptable terms. And bring to witness two just men from among you and
establish the testimony for [the acceptance of] Allah . That is
instructed to whoever should believe in Allah and the Last day. And
whoever fears Allah - He will make for him a way out
[At-Talaq: 2]
More information :
http://en.wikipedia.org/wiki/Divorce_%28Islamic%29