With around 7 trillion barrels reserves and recent increase in oil demand, there is no doubt that there would be tremendous effort on the development of heavyoil/bitumen (HO-B) reservoirs in the next decades. Yet the in-situ recovery of HO-B is still not a simple process and there are many technical challenges accompanied with it.Two major techniques, namely thermal and miscible, have been considered in the HO-B development, along with several other auxiliary methods (chemical, gas, electromagnetic heating etc.) for different well configurations, steam assisted gravity drainage (SAGD) being the most popular among others. Miscible techniques did not yet go to a high commercial level, while thermal techniques have by far a stable foundation in the industry.Despite remarkable amount of laboratory experiments and computational studies on the thermal techniques for HO-B, especially SAGD, there was no extensive and critical literature review of the knowledge gained over almost three decades. We believe that a critical review of the status of the SAGD process will fill the gap by shedding light on the deficiencies and limitations of the process, further development areas, and new research topics. Specific attention, in this paper, was given to (a) the effect of geological environment on the physics of the process, (b) evaluation of the laboratory scale procedure and results (reasons of residual oil saturation, is it well configuration or pore scale dynamics?) and the reasons of the inconsistency between the lab and field scale performances, (c) problems faced in numerical modelling (capturing the physics of the process, relative permeability curves, dynamics of gravity controlled counter-current flow), (d) evaluation of the pilot and commercial level field applications, and (e) operational and technical challenges.It is believed that a good compilation of the records produced over three decades will constitute a useful reference for the industry and academic people.