Book excerpt: Natural and Semi-Natural Grassland Ecosystems (NSG) represent high-value biodiversity hotspots for biodiversity of the European continent, as well as an invaluable cultural heritage forged through millennia of human-nature interactions. While pristine natural European grasslands result mainly from constrained specific climatic and soil conditions, semi-natural grasslands largely result from the activities of humans and their livestock (e.g. grazing, mowing, burning) during millennia of low-intensity land use. European NSG, their biodiversity, and the cultural heritage they represent are highly threatened since the beginning of the 20th century in a context of multifactorial global change including environmental dimensions (climate change, habitat fragmentation, pollution, biological invasions) and land-use changes with the accelerating of socio-economic evolution of agricultural practices (intensification or abandonment) and urbanization.