There have been three different iterations of the 14-42mm:
- II: This revision added a bayonet that supports add-on converters at the front of the lens
- IIR: This revision hides the bayonet with a removable ring and reportedly also has a faster AF motor, which helps with the third-generation Olympus autofocus system (e.g. E-P3, E-PL3, E-PM1)
Optically they all appear to be identical in performance (other than focus).