The Internal Revenue Code and the Title I of ERISA (administered by the U.S. Department of Labor) have restrictions on how retirement plan assets can be invested. For example, certain investments will cause UBTI (unrelated business taxable income) to what is otherwise a tax-exempt trust. Certain investments may cause prohibited transactions with the resulting excise tax under IRC Section 4975. There are also the general fiduciary rules governing trustees generally, e.g., the duty to diversify. This handout is designed to advise the trustee and the plan sponsor on how to avoid the pitfalls.