In the high Andes, which have been the cradle of important pre-Hispanic civilizations and are inhabited by millions of people, glacier losses consecutive to warming result in the emergence of large proglacial landscapes (‘tierras nuevas’; + 8000 km2 since 1850), which generate both threats and opportunities for adaptation. Risks include species extinctions, loss of water provision, water contamination from acid rock drainage, slope instability, reduction of biomass for livestock and loss of identity and cultural values. Novel ecosystems, however, are emerging after the retreat of the ice, and can mitigate the risks related to climate change: they are the future providers of key Nature’s Contributions to People (NCPs) for the local populations, which are currently provided by downstream support ecosystems. The speed of glacial retreat far exceeds that of the vegetation primary succession and soil formation. As a result, the novel proglacial ecosystems might not fully supersede the role played by the current support Andean ecosystems, which are fragilized by global changes. Will these novel ecosystems be able to mitigate socio-economic and ecological crises caused by the acceleration of global change? Do they require intervention to enhance NCPs provision? In the high Andes, ancestral practices (Andean camelid herding, terracing, irrigation) have been used for millennia to enhance the sustainability and productivity of high Andean ecosystems, but it has been scarcely used in proglacial landscapes so far. Such practices have the potential to enhance the NCPs provided by novel ecosystems, such as limiting water contamination, increasing biomass production for livestock and slope stability. The objective of the project TierrasNuevas is to co-construct and evaluate the reasonable implementation of in situ, ancestral Nature-based Solutions (NbS) in proglacial landscapes that can mitigate the negative consequences of glacier retreat on NCPs. For this purpose, we are an inter- and trans-disciplinary consortium that brings together specialists in Human, Earth and Life sciences. The consortium (UMR AMAP, IGE and CESCO; gender ratio = 1) will collaborate with local communities and with long-standing academic and non-academic Andean partners with extensive experience in the focal sites. The project will be carried out in four flagship valleys inhabited by local communities who still use ancestral land-use practices in four mountain ranges in Peru (1), Bolivia (2) and Chile (1). The results collected in the flagships valleys will be exportable to the subwatershed and mountain ranges scales, conferring a regional scope of the project. TierrasNuevas is built around three work packages (WPs). WP1a, in collaboration with Peasant Communities, co-assesses the local needs for investigations and proposes ancestral NbS to be tested with in situ experiments in WP3. WP2 characterises the landscapes at three spatial scales: the four flagship valleys, their glacierized subwatersheds, and their mountain-range (geo-physical and socio-economic mapping, including the characterization of the support ecosystems). WP3 implements and evaluates the in situ experiments co-constructed in WP1a in proglacial landscapes (vegetation, soil, water quality). Outcomes of WP2 and WP3 are later combined to compare the NCPs delivered by support ecosystems and novel proglacial ecosystems and to upscale results to subwatersheds and mountain ranges. The results are ultimately co-evaluated with stakeholders and decision-makers to propose decision-making tools (WP1b). In conclusion, TierrasNuevas is a co-constructed project that responds to a strong societal demand on a regional scale and will have a direct impact on management practices and on the socio-economic sustainability and cultural identity of peasant communities in the Andes.