Meeting Rationale. In October 2023, the international community of who use marine invertebrates as research models to address fundamental questions in developmental, cell, ecological, and evolutionary biology will meet for The Developmental Biology of the Sea Urchin and other Marine Invertebrates (DBSUMI). This will be the 27th forum for this meeting, which has been held approximately every 18 months since 1980. Throughout the years, these meetings featured topics relevant to a broad range of biologists working on subjects ranging from gamete interactions, egg activation, cell fate determination and patterning, axis specification, gene expression, genomics, morphogenesis, cell signaling, evolution, ecology, immunology, neurogenesis, regeneration and experimental technology. Importantly, advances in these fields apply not only to sea urchins but more broadly across biological systems. To facilitate these broad findings, the original “sea urchin community” has intentionally expanded the field by inviting researchers working on the cell and developmental biology of other marine invertebrate models including tunicates, hemichordates, cephalochordates, molluscs, polychaetes, cnidarians, ctenophores, and sponges. Each model has its own unique ability to answer fundamental questions that can solve questions related to human development, health and disease. The conceptual basis of comparative studies lies in their ability to identify commonalities of mechanisms and processes across multiple taxa, which in turn reveal unifying principles of biology. Famous examples for major discoveries arising from studies in marine organisms include our knowledge of cell divisions and cyclins, and the role of microtubule motor kinesins, and the development of GFP and other fluorescent proteins as widely-used tools in biomedical science. Thus, our goal is to establish DBSUMI as the “must attend” conference for labs using marine invertebrate model systems to answer a broad range of questions that are highly relevant to human development and health. One central focus of the program is to facilitate in-depth discussions among scientists. The combination of talks, discussion periods, and informal social gatherings allow the integration of findings from diverse systems. DBSUMI XXVII and its future iterations will be indispensable for the growth and vitality of this scientific community, as unique comparative approach across a wide range of marine invertebrate models is underrepresented at any cell, evolutionary and/or developmental biology meetings. To continue expanding and modernizing the meeting, the organizers are introducing new initiatives and seeking NIH meeting funding to support their implementation. Specific Objectives. We are inviting more PIs, post-docs, and graduate students from non-sea urchin labs to this meeting than in previous iterations. Many of these labs use aquatic models for human disease with NIH-funded research programs (e.g. within NIGMS, NIEHS, NI...