Diabetes is one of the major medical problems in the world. The discovery of insulin was a milestone in the history of medical science. This legendary invention has completed 100 years of its journey. Through this 100-year journey, many important events have taken place, and many modifications have been made to make it convenient for commercialization and patient compliance. After the antidiabetic activity of the pancreatic extract was discovered, the bovine and pork insulin came into use. Then, recombinant human insulin was discovered. Now long-acting to rapid-acting insulin forms are available (e.g., insulin pens, insulin pumps, and the like), and different systems are in use to deliver them to the body, but all these insulins are in invasive dosage forms and have some disadvantages, too. As we are using the oral form of most medicines, we prefer the oral form of insulin. Therefore, the concern is now to develop the oral dosage form of insulin. Some proposed oral dosage forms are at different stages of the clinical trial such as classical dosage forms, enzyme inhibitors, unnatural amino acids, nanoparticles, cell-penetrating peptides, and so on. Since the oral forms of insulin create some limitations and confusion, further research is required to solve these problems. Accordingly, the aim of the review was to predict the possibility of developing marketable oral insulin.