The Mexican Institute of Social Security has a legal mandate derived from Article 123 of the Political Constitution of the Mexican United States. Its mission is to be the principal instrument of social security, and serve as a public service provider for all workers and their families. Furthermore, the Institute is constitutionally mandated to pursue a continual extension in its coverage and therefore contribute to the creation of the welfare state for all Mexicans.

Moreover, Article 2 of the Social Security Law (SSL) establishes that the purpose of social security is to guarantee the right to health, medical assistance, livelihood, and the necessary social services for individual and collective well-being. It is also responsible for the provision of pensions backed by the State upon fulfilling their legal requirements. With this understanding, the Institute provides a range of insurance services, thus complying with its legal mandates, and above all, affording tranquility and stability to workers and their families in the face of events identified in the SSL. Insurance is offered to users registered under the Obligatory or Voluntary Regimes. The benefits, requirements and contributions vary in each Regime and are clearly defined in the SSL.

The SSL conceives IMSS as an autonomous organism whose operation is divided in two main branches: i) a risk-management institution, and ii) a service providing entity.

As a risk-management institution:

The Institute administers the various branches of insurance provided under the SSL. This role requires the management of contributions and financial resources in order to provide benefits in cash and specie. As a fiscally autonomous organism, the Institute must conduct an effective collection while achieving transparency and control in the information generated.

As a service provider:

The Institute promotes the health of the insured working population, worker's families, pensioners and students through a comprehensive system of services that includes preventive and curative medical services; childcare, and economic and social benefits provided for under the SSL.