The relative effectiveness of blowing and suction in controlling separation and circulation is assessed in the present paper. The paper focuses on low momentum input where suction is much superior to blowing in generating lift and decreasing drag. Blowing is mostly deleterious at levels of input that result in the jet velocity being comparable to the free stream's velocity and this paper attempts to explain this effect. Furthermore, the significance of slot width, slot location and the bluntness of the trailing edge are discussed. The effectiveness of suction is generally improved by widening the slot, moving it downstream and reducing the bluntness of the trailing edge. The effectiveness of blowing is best realized when the slot is located near the natural separation point for the narrowest slot possible. There is a threshold input of momentum where blowing becomes more effective than suction. Most of the data presented was taken at incompressible speeds and at Re < 2.5*10 5.