Collisions of atoms and molecules are required for bond formation and are thus key to any chemical reaction. Their outcome is determined by the collision energy, relative orientation, and impact parameter of the reactants. Collision studies in the gas phase have shown that energies are easily controlled, whereas molecular orientations are difficult to steer and the impact parameter is completely uncontrollable. Here, we study collisions of individual molecules at a surface, in which each compound is imaged before and after the collision by scanning tunneling microscopy, thereby allowing precise control of orientations and impact parameters. We observe that the molecules must collide within a narrow reaction cone, and that surface-atom displacements can enable a reaction even for disfavored pathways.  For more details, see.