Alpine grassland and nival zones are characterized by variable environmental conditions, compressed breeding seasons, and limited resources such as food and nest site availability. As a result, high elevation habitats around the world contain an impressive diversity of unique bird species, highly specialized to thrive in challenging environmental conditions with limited breeding opportunities. In this chapter, we highlight the global diversity of alpine habitats and avifaunal communities. We first define general features of alpine and nival zones, before providing an overview of these habitats across 10 major regions around the world. Assembling a global list of alpine breeding birds, we then summarize what makes alpine avifauna unique and how communities vary regionally. Specifically, we focus on traits that characterize how species interact with their environment: i) alpine specialization and endemism, ii) nesting strategies, and iii) migration behaviour. Finally, we address some of the main eco-evolutionary drivers that shape these alpine communities, including climate, vegetation structure, food availability, and species interactions. We conclude by discussing the critical role snow dynamics play in maintaining many alpine bird communities and highlight the concerning trends associated with a rapidly changing climate that are putting pressure on alpine birds.