The systematic documentation, discovery, and reuse of mathematical models ? especially across disciplines ? is a challenging problem. To address this problem we present MathModDB, an ontology-based database and knowledge graph for mathematical models. MathModDB has recently been integrated within the MaRDI Portal web-service and currently comprises 20,000 semantic statements on over 200 mathematical models from a variety of academic disciplines. These include use cases from chemical reaction kinetics, semiconductor and plasma physics. Future work will focus on community-driven contributions and curation, as well as integration with scientific computing tools chains, workflow systems (e.g. Snakemake) and other domain-specific knowledge graphs (e.g., Plasma KG, in cooperation with the Leibniz Institute for Plasma Science and Technology, Greifswald). We will offer a hands-on demonstration on model documentation using MathModDB during the poster session.