The Thrift Savings Plan (TSP) is a defined contribution plan for United States civil service employees and retirees as well as for members of the uniformed services. As of December 31 2013, there were approximately 4.6 million participants, and nearly $407 billion in assets under management. The TSP is one of three components of the Federal Employees Retirement System (FERS; the others being the FERS annuity and Social Security) and is designed to closely resemble the dynamics of both private sector 401(k) and Roth 401k (new Roth TSP implemented in May 2012) plans. It is also open to employees covered under the older Civil Service Retirement System (CSRS). The TSP is administered by the Federal Retirement Thrift Investment Board.