In session II you have learnt the anesthesia machine with its component part. The anesthetist should be familiar to anesthesia machine and breathing system to use it effectively and to care and maintain at user level. Although the anesthetic breathing system is a part of anesthesia machine, it was very difficult to cover important points of anesthesia machine with breathing system in one session as one competency. Therefore we present the breathing system and other parts in this session. Mixture of gases from the flowmeters and vaporizer exits the anesthesia machine at the common gas outlet; it then enters an anesthetic breathing circuit. The function of the anesthesia breathing circuit is not only to deliver oxygen and anesthetic gases to the patient, but also to eliminate CO2. In this session different types of breathing system, the use of carbon dioxide absorber and the scavenging system will be discussed therefore it will equip you with relevant knowledge, skill and appropriate attitude to use anesthesia machine with its breathing system effectively.