Noting a lack of broad empirical studies on subject repositories, the authors investigate subject repository trends that reveal common practices despite their apparent isolated development. Data collected on year founded, subjects, software, content types, deposit policy, copyright policy, host, funding, and governance are analyzed for the top ten most-populated subject repositories. Among them, several trends exist such as a multi- and interdisciplinary scope, strong representation in the sciences and social sciences, use of open source repository software for newer repositories, acceptance of pre- and post-prints, moderated deposits, submitter responsibility for copyright, university library or departmental hosting, and discouraged withdrawal of materials. In addition, there is a loose correlation between repository size and age. Recognizing the diversity of all subject repositories, the authors recommend that tools for assessment and evaluation be developed to guide subject repository management to best serve their respective communities.