  Topological quantum field theories can be used to probe topological
properties of low dimensional manifolds. A class of these theories known as
Schwarz type theories, comprise of Chern-Simons theories and BF theories. In
three dimensions both capture the properties of knots and links leading to
invariants characterising them. These can also be used to construct
three-manifold invariants. Three dimensional gravity is described by these
field theories. BF theories exist also in higher dimensions. In four
dimensions, these describe two-dimensional generalization of knots as well as
Donaldson invariants.
