| Heegaard Floer homology can be very fruitfully applied in studying various questions in contact topology. We review the definition of the invariant of a contact structure on a closed 3--manifold, and outline the definition of a new invariant of Legendrian knots, taking values in the knot Floer homology of the underlying null-homologous knot. With the aid of this invariant we discuss transversal simplicity of knots in many (possibly overtwisted) contact structures, and in particular show that the Eliashberg-Chekanov twist knots (e.g. the 7_2 knot in Rolfsen's table) are not transversely simple. |