The National Social Security and Insurance Trust (NASSIT) was established through an Act of Parliament and is charged with the responsibility of administering the Sierra Leone Pension Scheme. NASSIT started full operations in January 2002 as a partially funded defined benefit pension plan which requires a member to contribute for at least 180 months on/before they retire at age 60 to qualify for full retirement pension.

At the inception of the scheme, a transition period was defined, which spanned from 2002 to 2006. During this transition period, arrangements were made to enhance the pension rights of members who, based on their ages at the inception of the scheme, were very unlikely to meet the 180 months contributions qualifying conditions for full retirement pension. The transitional arrangements included the Grandfathering provision, which allowed members in the private sector to gain additional free credits months; the Validation of Past Services for government employees on the Accountant General's payroll as at January 2002; and the Purchase of Credits to top up credits that were less than the required amounts to acquire full pension rights.