Restoring mountain ecosystems was the theme of International Mountain Day 2023 on 11 December.

This theme was selected to fully include mountains in the UN Decade on Ecosystem Restoration 2021–2030, co-led by the Food and Agriculture Organization of the UN and the UN Environment Programme. The Decade is an opportunity to draw together political support, scientific research and financial resources to significantly scale-up restoration and prevent further degradation of mountain ecosystems.

Mountains cover around 27 percent of the Earth's land surface and host about half of the world's biodiversity hotspots. As the water towers of the world, they supply freshwater to an estimated half of humanity. Mountains are home to an extraordinary range of plants and animals, and to many culturally diverse communities with different languages and traditions. From climate regulation and water provisioning services, to soil maintenance and conservation, mountains are key to our lives and livelihoods.

Yet mountains are suffering from the impacts of climate change and unsustainable development, escalating risks for people and the planet. Climate change threatens the flow of water, and fast-rising temperatures are forcing mountain species and the people that depend on these ecosystems to adapt or migrate. Steep slopes mean the clearing of forest for farming, settlements or infrastructure can cause soil erosion as well as the loss of habitat. Erosion and pollution harm the quality of water flowing downstream. According to the Intergovernmental Panel on Climate Change, up to 84 percent of endemic mountain species are at risk of extinction, while populations of a range of other montane plant and animal species are projected to decline and face extinction.

The UN General Assembly also recently proclaimed 2023–2027 "Five Years of Action for the Development of Mountain Regions" in its triennial resolution on sustainable mountain development. Its objectives are to attract grant assistance and investments for mountains, develop "green" economies and technologies, create mechanisms to strengthen cooperation between mountainous countries, and develop science and education in the field of sustainable mountain development.

International Mountain Day 2023 increased awareness about the relevance of mountain ecosystems and called for nature-based solutions, best practices and investments that build resilience, reduce vulnerability and increase the ability of mountains to adapt to daily threats and extreme climatic events.