Holomorphic disks and knot invariants

We define a Floer-homology invariant for knots in an oriented three-manifold, closely related to the holomorphic disk Floer homologies for three-manifolds defined in an earlier paper. We set up basic properties of these invariants, including an Euler characteristic calculation, behaviour under connected sums. Then, we establish a relationship with $H{F}^{+}$ for surgeries along the knot. Applications include calculation of $H{F}^{+}$ of three-manifolds obtained by surgeries on some special knots in $S^3$, and also calculation of $H{F}^{+}$ for certain simple three-manifolds which fiber over the circle.