Substantial attention has been given to the issue of access to medicines for communicable diseases; however, access to essential medicines for diabetes, especially insulin, has had insufficient focus. Although insulin was discovered in 1921, the drug is unattainable to many globally, and this Review aims to highlight the range and complexity of factors that contribute to this unattainability. Manufacturers' selling prices of various insulin formulations and presentations, duties, taxes, mark-ups, and other supply chain costs affect the price of insulin and hence the drug's affordability to health systems and individuals. Unlike drugs for HIV and AIDS, the production of generic or biosimilar insulin has not had an effect on the overall market. Other factors contributing to poor availability of insulin include its quantification at the national level, in-country distribution, and determination of needs at lower levels of the health system. Although insulin is essential for the survival of people with type 1 diabetes and is needed for improved management of diabetes for some people with type 2 diabetes, very little has been done globally to address the issue of access, despite the UN's political commitment to address non-communicable diseases and ensure universal access to drugs for these disorders.