The Library Endowment Trust is a nonprofit 501(c)(3) organization which provides the general public with a tax-deductible vehicle whereby contributions will be invested on a permanent basis. The Trust is one of three partners focused on library service and support for the Metropolitan Library System. It was created in 1986 by the Friends of the Library through committee meetings that included officers of the Friends, several Library Commissioners and interested citizens. The goal of creating an endowment was to have an entity to do the following:
- Invite and invest monetary gifts of all sizes in permanent funds that will grow and be used to benefit the Metropolitan Library System.
- Distribute earned income annually for the benefit of Oklahoma County library customers of all ages and stages of life, based on a "wish list" of materials or projects desired, provided by Metropolitan Library System Executive Director.
- Oversee fiduciary aspects of the Endowment via 15 Trustees.
- There are also non-voting liaisons from both the Library Commission and from Friends of the Library.
- Fund its own expenses via an annual budget and reimburse MLS for staff hours spent exclusively on Trust business.
- Focus on creative ways to grow the funds seeded with money from generous library supporters from Oklahoma County and cities and states beyond.