Many institutions have open access policies that support, encourage, or require affiliated authors to make their publications openly accessible. The University of Minnesota adopted a policy that encourages open access to scholarly articles on January 1, 2015.
You can find a list of other institutional policies around the world at ROARMAP.
Some organizations that fund research, such as the UK's Wellcome Trust and the Gates Foundation, require that published results be made openly available—such requirements are often referred to as "open access" or "public access" policies. US Federal government granting agencies have evolving requirements for researchers. To learn more, explore Federal Public Access Requirements.