A system for generating shockwaves comprising: an axially extending elongate member; a balloon (106, 564) surrounding a portion of the elongate member, said balloon (106, 564) being fillable with a conductive fluid; a first electrode assembly at a first location along the length of the elongate member, the first electrode assembly having a first inner electrode, a second inner electrode, and an outer electrode and configured to initiate shockwaves at two circumferentially offset locations; and a second electrode assembly at a second location along the length of the elongate member, the second electrode assembly having a first inner electrode, a second inner electrode, and an outer electrode and configured to initiate shockwaves at two circumferentially offset locations wherein the second inner electrode of the first electrode assembly and the first inner electrode of the second electrode assembly are connected and wherein when the balloon (106, 564) is filled with the conductive fluid and a voltage is applied across the first inner electrode of the first electrode assembly and the second inner electrode of the second electrode assembly, a current flows in series from the first inner electrode to the outer electrode to the second inner electrode of the first electrode assembly to the first inner electrode to the outer electrode to the second inner electrode of the second electrode assembly such that a first pair of shockwaves is generated at the two circumferentially offset locations of the first electrode assembly and a second pair of shockwaves is generated at the two circumferentially offset locations of the second electrode assembly. an axially extending elongate member; a balloon (106, 564) surrounding a portion of the elongate member, said balloon (106, 564) being fillable with a conductive fluid; a first electrode assembly at a first location along the length of the elongate member, the first electrode assembly having a first inner electrode, a second inner electrode, and an outer electrode and configured to initiate shockwaves at two circumferentially offset locations; and a second electrode assembly at a second location along the length of the elongate member, the second electrode assembly having a first inner electrode, a second inner electrode, and an outer electrode and configured to initiate shockwaves at two circumferentially offset locations wherein the second inner electrode of the first electrode assembly and the first inner electrode of the second electrode assembly are connected and wherein when the balloon (106, 564) is filled with the conductive fluid and a voltage is applied across the first inner electrode of the first electrode assembly and the second inner electrode of the second electrode assembly, a current flows in series from the first inner electrode to the outer electrode to the second inner electrode of the first electrode assembly to the first inner electrode to the outer electrode to the second inner electrode of the second electrode assembly such that a first pair of shockwaves is generated at the two circumferentially offset locations of the first electrode assembly and a second pair of shockwaves is generated at the two circumferentially offset locations of the second electrode assembly.