A 401k plan administrator is the person or company responsible for making sure a 401k retirement plan runs smoothly and follows all the legal rules. This includes tasks like handling employee enrollments, managing contributions, sending required notices, approving withdrawals or loans, and coordinating IRS filings and reports. The administrator also ensures that the plan stays in compliance with federal regulations and works with other parties like custodians, recordkeepers, and financial advisors. Sometimes the employer takes on this role, but it can also be outsourced to a third-party provider that specializes in plan administration.