An implantable stimulator (100, 101, 102, 103, 104, 105, 1110, 1111) comprising: - a pulse generator configured to generate at least one stimulation pulse; - a conformable foil-like substrate (300, 1400) having a longitudinal axis extending from the pulse generator to a distal end of the substrate (300, 1400), the substrate (300, 1400) comprising one or more adjacent polymeric substrate layers, the substrate having a first (310, 1410) and second (320, 1420) substantially planar surface; and - an electrode array (200, 400, 1220), proximate the distal end (300, 1400), having a first (200, 1220) and second (400, 1220) electrode comprised in the first (310, 1410) or second surface (320, 1420), located along the conformable portion of the substrate (300, 1420), each electrode (200, 400, 1220) in operation being configurable for transferring treatment energy, in use, to and/or from human or animal tissue; the implantable stimulator (100, 101, 102, 103, 104, 105, 1110, 1111) further comprising: - one or more electrical interconnections (250, 1210), between the pulse generator and the first (200, 1220) and the second (400, 1220) electrodes, for transferring electrical energy as one or more electrical treatment stimulation pulses to the coupled first electrodes and/or the second electrodes; wherein the one or more electrical interconnections (250, 1210) are positioned between the first (310, 1410) and second (320, 1420) surfaces of the substrate (300, 1400); wherein the conformable foil-like substrate (300, 1400) has a maximum thickness of 0.5 millimeter or less, proximate the first and second electrodes (200, 400, 1220),, the thickness being determined by a perpendicular distance between corresponding points on the first (310, 1410) and second outer planar surfaces (320, 1420), and wherein the substrate (300, 1400) and the pulse generator are embedded in one or more flexible bio-compatible encapsulation layers comprising Polydimethylsiloxane (PDMS). - a pulse generator configured to generate at least one stimulation pulse; - a conformable foil-like substrate (300, 1400) having a longitudinal axis extending from the pulse generator to a distal end of the substrate (300, 1400), the substrate (300, 1400) comprising one or more adjacent polymeric substrate layers, the substrate having a first (310, 1410) and second (320, 1420) substantially planar surface; and - an electrode array (200, 400, 1220), proximate the distal end (300, 1400), having a first (200, 1220) and second (400, 1220) electrode comprised in the first (310, 1410) or second surface (320, 1420), located along the conformable portion of the substrate (300, 1420), each electrode (200, 400, 1220) in operation being configurable for transferring treatment energy, in use, to and/or from human or animal tissue; - one or more electrical interconnections (250, 1210), between the pulse generator and the first (200, 1220) and the second (400, 1220) electrodes, for transferring electrical energy as one or more electrical treatment stimulation pulses to the coupled first electrodes and/or the second electrodes; wherein the one or more electrical interconnections (250, 1210) are positioned between the first (310, 1410) and second (320, 1420) surfaces of the substrate (300, 1400); wherein the conformable foil-like substrate (300, 1400) has a maximum thickness of 0.5 millimeter or less, proximate the first and second electrodes (200, 400, 1220),, the thickness being determined by a perpendicular distance between corresponding points on the first (310, 1410) and second outer planar surfaces (320, 1420), and wherein the substrate (300, 1400) and the pulse generator are embedded in one or more flexible bio-compatible encapsulation layers comprising Polydimethylsiloxane (PDMS).