A droplet actuator (110) comprising: one or more substrates (114, 116) arranged to form a droplet operations gap, the droplet operations gap comprising a region of gap height transition in which the gap height of the droplet operations gap transitions from a first gap height to a second gap height; and electrodes associated with the one or more substrates arranged for conducting droplet operations, the electrodes comprising a transition electrode which traverses the region of gap height transition. The electrodes may comprise electrowetting electrodes. The transition electrode may be flanked by first and second sets of electrodes having first and second footprint areas. The first footprint area may be greater than the second footprint area. The first set of electrodes may be arranged in a region of greater gap height and the second set of electrodes may be arranged in the region of lesser gap height.