  We study the topology of the space of smooth codimension one foliations on a
closed 3-manifold. We regard this space as the space of integrable plane fields
included in the space of all smooth plane fields. It has been known since the
late 60's that every plane field can be deformed continuously to an integrable
one, so the above inclusion induces a surjective map between connected
components. We prove that this map is actually a bijection.
