Knowledge gaps on forest soil processes and lack of a harmonised soil monitoring limit the EU’s ability to maintain soil related ecosystem services and to reach climate policy targets. A better understanding of the soil processes and a harmonised approach to manage and integrate data to computational models that are used for decision making is urgently required in order to meet climate and sustainability goals, including the UN's Agenda 2030 SDGs, the Paris Agreement of Climate Convention, the EU Bioeconomy Strategy, the EU's LULUCF Regulation, the EU Forest Strategy (2018), and the European Green Deal. HoliSoils will develop a harmonised soil monitoring framework and identify and test soil management practices aiming to mitigate CC and sustain provision of various ecosystem services essential for human livelihoods and wellbeing. HoliSoils incorporates novel methodologies and expert knowledge on analytical techniques, data sharing, soil properties and biodiversity, and processes with model development, in order to develop tools for soil monitoring, refine GHG assessment of the LULUCF sector, enhance efficiency of GHG mitigation actions, and improve numerical forecasting of soil-based mitigation, adaptation, and ecosystem services. HoliSoils applies a collaborative multi-actor approach, in order to maximise its applicability and impact beyond its duration. The multidisciplinary consortium consists of universities and research institutes from across Europe, with leading expertise on soil analysis and databases, development of advanced analytical techniques, complex system modelling, digital soil mapping, soil ecology, disturbance ecology, forest and GHG inventories, social sciences, and communications. It also involves active engagement with diverse stakeholders, including forest owners and managers, industry actors, forest extension services, a certification body, forest and soil researchers, climate policy support and GHG inventory experts, and policymakers.