Insulin is the most effective available medication for treating hyperglycemia in type 2 diabetes. If appropriately used, it can decrease any level of elevated HbA1C to, or close to, the desired goal. Whereas insulin therapy is required in all patients with type 1 diabetes, the decision of how and when to start insulin in type 2 diabetes is not as straightforward. Insulin usually should be started immediately in patients with marked weight loss, severe hyperglycemia, or ketosis. In the absence of these features, insulin should be added when glycemic goals are not met with one or more non-insulin agents, or when glycemic goals are unlikely to be achieved with non-insulin therapy. After the glucose is controlled and symptoms are relieved, it may be possible to withdraw the insulin or to be continued. Here, insulin therapy in patients with type 2 diabetes will be briefly reviewed.