Ligands mounted to surfaces via flexible polymer tethers represent a growing class of molecules used to engineer adhesion in drug targeting, biosensing, and self-assembling nanostructures. We show that the probability of end-functionalized grafted polymers binding to an opposing receptor is a strong function of the distance between the receptor and polymer anchor for many of the biopolymers and ligand / receptor pairs used in current research. Importantly, we find that the binding probability with respect to distance approximates a step function when 3 kT / L(kW)^1/2 << 1, where k is the Boltzmann constant, T is temperature, L is the polymer contour length, k is an effective polymer spring constant, and W is the ligand-receptor bond energy. This observation allows a number of analytical expressions to be derived to describe the rate, range, and strength of adhesion between surfaces bridged by tethered ligand-receptors.