Alpine ecosystems (alpine tundra) occur at a range of air density, water availability and seasonality worldwide on the treeless high terrain of mountains. They vary along geographic scales: boreal dwarf-shrub heaths, temperate sedge heaths, subtropical dwarf shrubs and tussock grasslands, and tropical giant forblands. Along local topographic gradients plant cover changes from windswept dwarf-shrub heath, to dense grass-sedge heath, to snowbank vegetation. These cold and relatively little exploited alpine ecosystems, nonetheless, are among those where climate warming impacts are forecast to be pronounced and detectable early on. We first review alpine life conditions and organism traits as a background to understanding climate impact related processes. Next, we provide an account of how alpine flora and vegetation have been impacted by recently observed climate change. Finally, a global network for long-term monitoring of climate-induced changes of vegetation and biodiversity in alpine environments is described.