The Ontology Summit is an annual series of events that involves the ontology engineering community as well as other communities related to each year's theme chosen for the summit. The theme for 2021 is *Ontology Generation and Harmonization* Ontologies are rich and versatile engineering artifacts. They can be extracted, learned, modularized, interrelated, transformed, analyzed, and harmonized as well as developed in a formal process. The Ontology Summit 2021 is exploring the many kinds of ontologies and how they can be manipulated. The summit consists of four tracks: Track A: The Ontological Landscape Track B: Definitions Track C: Neuro-Symbolic Learning Ontologies Track D: Sustainability of Ontologies The Ontology Summit is free and open to the public. No registration is required. All sessions are Zoom meetings on Wednesdays at Noon U.S./Canada Eastern Time. The Ontology Summit 2021 has already started, but every session is self-contained. The sessions are recorded, and the recordings and slide presentations are publicly available. To attend the meetings please see the information on the Ontology Summit 2021 Website at https://bit.ly/3gKukvC where one can find the schedule.