Environmental Control system (ECS) or Air management system plays a vital role in aircraft performance. Almost all military aircrafts are equipped with conventional - bleed air based ECS. For a single engine military aircraft, such a system results in an enormous ~1.2 MW of thermal power penalty over the engine. Electrical ECS (EECS) is revolutionary, rather evolutionary, since it affects many other systems. A lot of research has been carried out to incorporate EECS in civil airliners. But little has been done as yet in case of military aircrafts. There could be many reasons for the same like availability of electrical power on board, availability of eco-friendly refrigerants, high Avionics and Radar heat load, appropriate medium for condenser cooling etc. As electrical technology has gone through a lot of power density upgrades in recent decade specially, compared to pneumatic systems, it calls for a need to seriously work over electric ECS. However electric system has not yet achieved its mature stage and has its own limitation. If Electric ECS is used in military aircraft it would be the largest consumer of the Electric power. Presently, a combination of Conventional and Electric ECS called Hybrid ECS could be the best decision based on the available technology and as an intermediate step towards realisation of electric ECS for future aircrafts. This paper covers a brief description of conventional, electric and Hybrid ECS systems and compares them for military aircraft application. A special emphasis is given over the selection of refrigerant based on available cooling medium and electrical power on board for the electric ECS. Even after the Electric ECS simplicity, high performance and Low aircraft signature a lot challenges need to be addressed to make it feasible for combat high agility high speed military aircraft.