This deliverable outlines the CLEARING HOUSE typology of urban forests as nature-based solutions (UF-NBS). The typology thus conceptualizes entities relevant to UF-NBS. To do so, elements of green-blue infrastructure (GBI) are defined in the typology. Contrary to purely textual representations of knowledge, CLEARING HOUSE proposes a definition of GBI elements through traits, i.e., characteristic and defining morphological, physical, functional, and institutional attributes, including for example the composition, spatial grouping, and topology of UF-NBS elements, and the ecosystem services and benefits provided them. CLEARING HOUSE proposes a semantic approach to express this knowledge, i.e., a formalization of knowledge as an ontology using the Web Ontology Language. Such ontologies are machine-interpretable series of statements of facts to define a taxonomy (a vocabulary). The definitions of GBI elements are embedded within a formalization of overarching concepts, particularly, of urban forest, nature-based solutions (NBS), and of UF-NBS. Here, urban forest is conceptually understood as the entirety of trees within an urban-ecological system. NBS are perceived in CLEARING HOUSE as an overarching concept that embraces natural and semi-natural elements of the GBI such as forests, engineered solutions such as permeable pavements, as well as actions inspired by nature. UF-NBS are then conceptualized as the intersection of the two previous entities, i.e., as the intersection of urban forest and NBS, and thus include any tree-related NBS. The proposed typology will provide the grounding knowledge of the comparative case study analysis to be conducted by CLEARING HOUSE, and will serve as a basis for the development of the CLEARING HOUSE benchmarking tool.