Dissociative electron attachment (DA) to ClOCl is studied in a high resolution crossed beam experiment. Two complementary ion pairs, Cl-/ClO- and O-/Cl-2(-), are observed. The Cl-/ClO- pair arises from a simple Cl-OCl bond cleavage with the electron sitting on either of the two fragments. The O-/Cl-2(-), pair is formed by a concerted reaction with the expulsion of O- (or O) and formation of Cl-2 (or Cl-2(-)). Ab initio calculations indicate that in low energy electron attachment an electronically excited state of the precursor anion (ClOCl-. (B-2(2))) is involved.