Missionaries and Cannibals

Three distressed missionaries wish to take three cannibals across a wide river.

They are restricted, however, by the following conditions:

(1) They have only one boat.

(2) Only 2 people can ride in the boat for each crossing.

(3) All missionaries but only one cannibal can row the boat.

(4) There must never be fewer missionaries than cannibals on one side, for the cannibals will feast on the missionaries.

(Count any people in the boat when it is on a given side as members of the group on that side).

How do they all cross the river?