The NFDI MatWerk Ontology (MWO) and the accompanying Materials Science and Engineering Knowledge Graph (MSE-KG) are central pillars of the NFDI-MatWerk initiative, a national research data infrastructure project in Germany [1]. Their joint purpose is to establish a semantically rich, interoperable, and sustainable digital ecosystem for managing, sharing, and reusing research data in the field of Materials Science and Engineering (MSE). By combining the expressive power of ontologies with the connectivity of knowledge graphs, this infrastructure enables deeper integration, querying, and reasoning over diverse datasets and research artifacts [2]. The MWO provides a domain-level ontology based on the Basic Formal Ontology (BFO 2020) [3,4] and adopts core modules from the NFDIcore mid-level ontology [5], ensuring logical consistency and alignment with cross-domain standards. It supports the annotation and integration of data related to the materials science lifecycle — including materials, processes, properties, experiments, software, instruments, people, and institutions. It also describes the organizational structure of the NFDI MatWerk consortium itself (working areas, use cases, partner projects), forming a basis for introspection and collaboration. To promote modularity and reusability, the MWO builds on semantic web principles and aligns with existing vocabularies and upper ontologies, allowing entities to be referenced and linked beyond project boundaries. This fosters harmonization between MSE-related datasets and contributes to interdisciplinary knowledge integration, especially relevant in large-scale data infrastructures like the NFDI. Built on top of the MWO, the MSE-Knowledge Graph (MSE-KG) is developed as a central knowledge base that connects entities across data portals, publications, workflows, and community assets [6]. It acts as a gateway to semantically enriched and interlinked data from the NFDI MatWerk ecosystem, using W3C-compliant technologies such as RDF, OWL, and SPARQL. The MSE-KG is hosted on a customized Wikibase instance, providing an interactive platform where stakeholders can collaboratively edit, curate, and visualize knowledge related to MSE research. Key features of the MSE-KG include: Representation of research outputs, such as datasets, publications, metadata schemas, and ontologies. Linking of people, organizations, and research projects to their outputs and domains of expertise. Integration of software tools, data repositories, and experimental workflows to support reproducible science. Alignment with FAIR principles, ensuring that data is Findable, Accessible, Interoperable, and Reusable. By combining ontological formalism with knowledge graph technologies, the MWO and MSE-KG enable powerful applications such as semantic search, data-driven decision support, and automated reasoning across distributed research data. They not only provide the semantic backbone for the NFDI MatWerk initiative but also serve as an open framework for other communities within and beyond the materials science domain to adopt and build upon. In summary, the NFDI MatWerk Ontology and Knowledge Graph embody the transition from isolated data silos to a shared semantic infrastructure, accelerating research, enhancing collaboration, and fostering innovation in materials science and engineering.