The SeaLiT Ontology is a formal ontology intended to facilitate the integration, mediation and interchange of heterogeneous information related to maritime history. It aims at providing the semantic definitions needed to transform disparate, localised information sources of maritime history into a coherent global resource. It also serves as a common language for domain experts and IT developers to formulate requirements and to agree on system functionalities with respect to the correct handling of historical information. The ontology uses and extends the CIDOC Conceptual Reference Model (ISO 21127:2014), in particular version 7.2.1, as a general ontology of human activity, things and events happening in space and time. The ontology has been developed following a bottom-up process from primary data collected in the context of the SeaLiT Project (Seafaring Lives in Transition, Mediterranean Maritime Labour and Shipping, 1850s-1920s). SeaLiT is an international research project, funded by the ERC Starting Grant 2016, which explores the transition from sail to steam navigation and its effects on seafaring populations in the Mediterranean and the Black Sea between the 1850s and the 1920s. More information about the construction of the SeaLiT Ontology, the considered data sources, as well as their transformation to a knowledge graph using the SeaLiT Ontology, can be found in the following papers: P. Fafalios, A. Kritsotaki, and M. Doerr, "The SeaLiT Ontology – An Extension of CIDOC-CRM for the Modeling and Integration of Maritime History Information". ACM Journal on Computing and Cultural Heritage, 2023. https://doi.org/10.1145/3586080 [pdf, bib] P. Fafalios, K. Petrakis, G. Samaritakis, K. Doerr, A. Kritsotaki, Y. Tzitzikas, and M. Doerr, "FAST CAT: Collaborative Data Entry and Curation for Semantic Interoperability in Digital Humanities", ACM Journal on Computing and Cultural Heritage, 2021. https://doi.org/10.1145/3461460 [pdf, bib] The (resolvable) namespace of the ontology is: http://www.sealitproject.eu/ontology/ An OWL implementation of the ontology is available at: https://sealitproject.eu/ontology/SeaLiT_Ontology_v1.2.owl Knowledge graphs that make use of the SeaLiT Ontology are available at: https://zenodo.org/record/6460841. These RDF datasets integrate information of 16 different types of archival sources related to maritime history, including crew lists, payrolls, registers of different types, censuses, and employment records.