PhySH (Physics Subject Headings) is a physics classification scheme developed by the American Physical Society to organize journals, meetings, and other content by topic. The development of PhySH is motivated by the lack of a fully open, high quality classification scheme for physics. It is intended initially to meet the specific goals of the APS for our journal, meeting, and other content. A longer term goal is to make it available for use by the broader community. (...) Right now, the main use of PhySH is to classify manuscripts within the APS peer-review process and, ultimately, published journal articles. The assigned concepts will be used for ensuring articles are routed to the most appropriate handling editor who is knowledgeable in that area. They also help editors in finding similar articles previously submitted and in finding suitable referees. As one might expect with something so new, the refinement of PhySH is still very much underway. The facets and disciplines have been identified and almost 3,000 concepts have been added to PhySH through an iterative process that is still ongoing. Many APS journal editors are involved in this process, primarily by lending their expertise in the various subfields in physics. The assignment of concepts to the various facets can be rather subjective. Thus, we expect to make many adjustments to PhySH as we receive feedback from the community (especially authors using PhySH to classify their submissions) and as we incorporate PhySH into the APS journal websites. As we iteratively refine PhySH over the coming months, the rate of new concept additions, concept reassignments within facets, and new relationships among concepts should abate significantly.