Tree diversity is assumed to increase the stability of the functional processes in forests, making them more resilient to increasing stress factors. Such effect is assured by a combination of factors including niche complementarity, ecological insurance and interaction between functional traits. The ecological stability is the condition to make constant the provision of ecosystem services. Specific ecosystem services are related to specific functions, and functions are connected to a combination of functional traits. The cause-effects relationships between functional traits – functional processes and ecosystem services represent a challenging issue to promote a multifunctional silviculture under climate change scenarios. These relationships are currently studied within international experimental/observational networks and projects, such as TreeDivNet (experimental plantations specifically established with different degrees of diversity) and FunDivEUROPE (7FP project that includes plots in mature forests within a climatic gradient in 6 European forests from boreal to the Mediterranean region). Moreover new criteria and methods have been developed to explore at large scale the role of forest diversity by using the data coming from the National Forest Inventories (NFI) and the ICP-Forests Level I network (forest condition monitoring). Effects of tree diversity, and related functional traits, have been investigated for tree growth, carbon sequestration and the response to drought. With this communication the authors report the state-of-the-art about the studies concerning the role of functional forest diversity in delivering ecosystem services and the ongoing scientific initiatives.