Insulin is a hormone that is exclusively produced by pancreatic beta cells. Beta cells are located in the pancreas in clusters known as the islets of Langerhans. Insulin is response to changes blood glucose concentration. Due to lack of insulin in our body, we are taking insulin in the form of injection or inhalation. Inhalable insulin was available from September 2006 to October 2007 in the United States as a new method of delivering insulin, a drug used in the treatment of diabetes, to the body. After the withdrawal of the only inhalable formulation, all currently available insulin formulations are administered by subcutaneous or intravenous injection. A new inhalable insulin product was approved. Inhaled insulin is a novel route of insulin administration which has the potential to become a therapeutic option in the treatment of both Type I Diabetes mellitus and Type II Diabetes mellitus. Overall the clinical trials have demonstrated that inhaled insulin is no inferior to subcutaneous insulin for improving glycemic control.