Ablation devices comprising elongated flexible members that are repositioned to at least partially surround tissue to be ablated. The exemplary ablation instruments utilize rigid or semi-rigid devices that are either affixed to the flexible member or repositionable along the flexible member. The clamping and ablating surfaces include electrodes or other means for delivering ablation energy. The electrodes may be brought into proximity with each other so as to provide a uniform force profile across the tissue to be ablated. In such a circumstance, once the tissue between the clamping and ablating surfaces is compressed, the electrodes are activated to create an ablation lesion.