  We give a fresh introduction to the Khovanov Homology theory for knots and
links, with special emphasis on its extension to tangles, cobordisms and
2-knots. By staying within a world of topological pictures a little longer than
in other articles on the subject, the required extension becomes essentially
tautological. And then a simple application of an appropriate functor (a
`TQFT') to our pictures takes them to the familiar realm of complexes of
(graded) vector spaces and ordinary homological invariants.
