  We discuss the relations between (topological) quantum field theories in 4
dimensions and the theory of 2-knots (embedded 2-spheres in a 4-manifold). The
so-called BF theories allow the construction of quantum operators whose trace
can be considered as the higher-dimensional generalization of Wilson lines for
knots in 3-dimensions. First-order perturbative calculations lead to higher
dimensional linking numbers, and it is possible to establish a heuristic
relation between BF theories and Alexander invariants. Functional
integration-by-parts techniques allow the recovery of an infinitesimal version
of the Zamolodchikov tetrahedron equation, in the form considered by Carter and
Saito.
