The global biodiversity crisis has stimulated decades of research into the causes and consequences of biodiversity. These studies have yielded key insights into species coexistence and the functional consequences of biodiversity change, establishing that biodiversity is fundamental to enhancing the temporal stability of ecosystem functioning. However, these insights have largely been derived from studies conducted at small spatial scales and over short time periods. In this talk, I will address this gap by developing new theoretical frameworks to understand species coexistence and diversity-stability relationships across scales. Specifically, I will present new criteria for species coexistence, and introduce a multi-scale framework to understand ecosyste stability and its relationship with biodiversity. I will then test predictions from these frameworks using empirical data from diverse taxa. Finally, I will discuss ongoing work aimed at bridging the cause and consequences of biodiversity by integrating coexistence theory with diversity-stability research.