This lecture will illustrate and teach the important concepts regarding post treatment assessment of rectal cancer after chemo-radiotherapy. Limitations, a key evolving concept will be stressed. T2, DWI and DCE will be included. At least 2 suggested systems for post treatment evaluation will be illustrated with discussion of their relative merits: mrTRG grading system and DWI + endoscopy systems. In particular, the growing trend towards Watch and Wait, AKA, non-operative management or organ sparing approaches will be discussed.