The author summarizes basic findings on the formation of insulin, its secretion and bond to insulin receptors and other phenomena at the post-receptor level. He summarizes basic indications for insulin treatment also beyond the sphere of diabetology. In a separate part the author summarizes briefly the history since the discovery of insulin up to the present time with modern therapeutic procedures (insulin injections, insulin pumps). The greatest part of the paper is devoted to contemporary insulin preparations and their use in therapy. A separate section is devoted also to insulin absorption and ways to influence its action. Attention is drawn to some differences in insulin absorption in relation to the site of injection, insulin concentration, body temperature and other factors which can be influenced. The objective of the paper is an overview of insulin and its use in therapy since to discovery of insulin to the present time.