Schemes are presented describing all possible rearrangement modes of cyclopentadienone‐dimers, the basic assumption being intramolecularity and C6‐C7 bond breaking in the (4π + 2π) dimers. For the endo‐dimer (2) all theoretically possible transformations (Fig. 1) are backed up by experiment. In the exo‐dimer (9) series (Fig. 3), some still await detection. Symmetry and stereochemical features are emphasized, as they enter structural and mechanistic considerations.