Smoking is responsible for damaging most of the organs of human body. It affects Lungs, Cardiovascular system, skin, Gastric System, Kidney, reproductive system, etc. But one organ that is affected most is Lungs, because this organ is in direct contact with smoke .Lungs are very essential for respiration purpose. Their main function is to supply oxygen to all tissues of body and release carbon dioxide that has been created throughout the body. Human lungs are two in number: left and right lungs .Right lung has three lobes and the left one is almost similar but with two lobes.Cigarette Smoking is the main reason to lung cancer because Cigarette smoke contains carcinogens, agents directly involved in causing cancer .In today’s world, it has been recorded that Smoking is responsible for around 80–90% of lung cancer cases.It is estimated that 87% of cases of lung cancer in the US are related to smoking.Passive Smoking is another main cause of Lung Cancer, where person himself is not involved in smoking but is living in environment of Smokers. So, we should take care of our surroundings as Cancer can occur in nonsmokers also. Those who live with smoker, have around 20-30% risk ,so it is better to prevent yourself and the smoker. Passive smoking results in around 3,400 deaths from lung cancer each year in the USA.Smoking is the main reason for disease called Chronic Obstructive Pulmonary disease or COPD where affected person finds tough to breathe because of blockage in airways.