If a non-spatiotemporal structure underlies space- time and the latter emerges from the former, then spacetime is not a fun- damental entity. Leaning on this, it has been defended that fundamental physical objects cannot be spatiotemporal (see, e.g., Wüthrich (2019)). How should the building relationship between fundamental physical ontology and spacetime then be understood? According to whether or not composition is adequate to grasp this relationship, some have proposed understanding it in mereological terms (see, e.g., Bihan (2018)), whereas others have advocated alternatives which overcome mereology (see, e.g., Baron (2021)). The work- shop aims to further explore the current metaphysical discussions concerning this relationship by considering different perspectives on the emergence of spacetime and how it relates to fundamental physical ontology, and in par- ticular whether that relationship is to be understood in mereological terms.