Thrift savings plans or TSP are tax deferred retirement savings and investment plans administered by the Federal Retirement Thrift Investment Board or FRTIB for federal employees. Thrift savings plans work on the same principle as 401 (k) plans offered by many private employers. All the employees who fall under the Federal Employees Retirement System or FERS and the Civil Service Retirement System or CSRS are eligible to participate in TSP. There are different requirements specified for both FERS and CSRS groups. Federal employees have to make voluntary contributions to their TSP accounts. Additionally, these contributions are not in any way considered a part of their regular FERS Basic Annuity or CSRS annuity contributions.