It is the action whereby responsible individuals contribute financial resources to the Social Security System by virtue of being included in said System because of exercising a labour activity.

Its basic elements are the contribution base, contribution rate and payment.

The obligation to pay contributions begins as soon as employment starts. Simply applying to register a worker has the same effect. Not presenting the application for registration/enrolment does not prevent the obligation to pay contributions from starting at the moment when the requirements for inclusion in the corresponding scheme are met.

It continues for the whole time that the worker carries out his or her activity. Obligation to pay contributions will continue in situations of:

• Temporary Disability.
• Risk during pregnancy and risk during breastfeeding.
• Maternity and paternity leave. 
• Fulfilment of public duties.
• Carrying out union representative duties (provided this does not cause an extended leave of absence from the job or termination of the activity).
• Time off or leave that does not cause extended leave of absence from the job.
• Special Agreements.
• Contributory unemployment.
• Welfare unemployment, if appropriate.
• In the cases established under the regulations of each scheme .

It ends when employment ends, provided this is reported in the correct way and within the specified time frame.

If termination is not requested or occurs after the deadline, the obligation to pay contributions will not end until the Social Security Treasury Office receives notice that the employment of the employed worker, the activity of the self-employed person or the situation that gave rise to inclusion in the Social Security Regime in question has ended.

The right of the Social Security Administration to determine debts due to contribution payments and any actions to demand payment of these debts, will expire after four years. The expiry period will be interrupted for normal reasons and, in all cases, by any administrative action carried out with the formal knowledge of the person responsible for the payment for the purpose of settling or collecting the debt and, especially, by administrative demand using debt reclaim or settlement procedures. (New version of article 21 of the General Social Security Act, in accordance with article 24 of Law 14/2000 of 29th December on Fiscal, Administrative and Welfare Measures).