Chern-Simons theory in the 1/N expansion has been conjectured to be equivalent to a topological string theory. This conjecture predicts a remarkable relationship between knot invariants and Gromov-Witten theory. We review some basic aspects of this relationship, as well as the tests of this conjecture performed over the last ten years. Particular attention is given to indirect tests based on integrality conjectures, both for the HOMFLY and for the Kauffman invariants of links.