In an era of unprecedented environmental change, the need for long-term, integrated ecosystem research has never been more urgent. The first eLTER Science Conference brings together a vibrant community of researchers, site and platform coordinators, and visionaries dedicated to understanding and safeguarding the complex systems that sustain life on Earth. This proceeding includes all contributions to the first eLTER Science Conference in June 2025 in Tampere, Finland. The Conference is a pivotal moment in our shared journey toward deeper understanding, collaboration, and stewardship of our planet’s complex socio-ecological systems. It marks an important milestone in the scientific work towards the Whole Systems Approach that is the unique foundation of the eLTER RI, addressing the Earth system at different spatial and temporal scales in order to answer many of the burning scientific and societal questions of our time. In the Anthropocene, environmental research is ever more challenged to develop a holistic approach for understanding the compounded impacts of the multiple stressors on our ecosystems, including, e.g., climate change, biodiversity loss, soil degradation, pollution, and unsustainable resource use. No scientific community can address these challenges in isolation from others. Therefore, the eLTER Science Conference is a unique opportunity to hear and see how different communities and disciplines gather forces to study not only the different spheres (geo-, hydro-, bio-, atmo-, and socio-sphere), but especially the linkages amongst them on the habitable skin of the Earth. The high-level scientific and social programme of the Conference encourages diversity of approaches, exchange between generations of scientists, and inclusivity in the spirit of promoting inter- and trans-disciplinarity. The presentations highlight the key elements of eLTER’s vision: advancing integrated, long-term environmental research, promoting interdisciplinary collaboration, and supporting policy-relevant science for sustainability. The workshops offer a chance for hands-on engagement with various practical subjects while also exploring themes through artistic perspectives. The Conference week is composed of high-level keynote lectures, oral and poster sessions, inspirational exhibitions, workshops, and field trips, relevant for researchers from Europe and globally. The transdisciplinary dialogue is forming an important, cross-cutting element to the Conference program. Altogether 335 participants from 44 countries and 226 institutions will contribute their latest findings to the programme. The 25 prominent Keynotes will address their own research themes in a broad and comprehensive manner. Early career researchers (83) ensure fresh perspectives and energy to continue the ongoing renewal of the scientific enterprise. Interestingly, a common thread runs through many of the sessions: the word ‘Integration’ features in the titles of seven of them. This highlights a strong, shared ambition among participants to deepen collaboration not just within their own disciplines, but across the wider research landscape. It underscores a collective push toward developing harmonised methods and tools that can support more impactful, high-quality science. At the same time, it sends a clear message to the broader environmental science community: eLTER is open for collaboration and eager to connect. Beyond the rich scientific agenda, the eLTER Science Conference offers a diverse and engaging social programme, including Conference dinner on a charming Viikinsaari island and four guided excursions, each offering a unique perspective on Finland’s diverse ecosystems and long-term ecological research initiatives, and providing participants with immersive experiences into Finland’s ecological research and conservation efforts. The Scientific Committee ensured the high-level scientific content of the Conference. The Organising Committee was led by Jaana Bäck and Jerome Gaillardet, and included Paulina Rajewicz, Nina Hobbhahn, Alexandra Tzvetkova, and Michael Mirtl; in addition, Benat Olascoaga Gracia, Allan Souza, Janne Korhonen, and Syed Ashraful Alam and the 12 conference assistants contributed to making the Conference a success. With this Proceedings, we welcome all authors and other attendees to the first eLTER Science Conference, a landmark event in shaping the future of integrated ecosystem, critical zone, and socio-ecological research across Europe and beyond. We thank all contributors and participants for their valuable insights and commitment, and we look forward to continuing this journey — united in eLTER’s vision for a more sustainable and resilient future. The conference is organised by the EU-funded eLTER PLUS Advanced Community project (Grant Agreement No. 871128) and supported financially by the University of Helsinki, the Federation of Finnish Learned Societies, Metsämiesten Säätiö Foundation, and the Atmosphere and Climate Competence Center Flagship of the Research Council of Finland.