Healthy ageing can be defined as "the process of developing and maintaining the functional ability that enables wellbeing in older age". Functional ability (i.e., the health-related attributes that enable people to be and to do what they have reason to value) is determined by intrinsic capacity (i.e., the composite of all the physical and mental capacities of an individual), the environment (i.e., all the factors in the extrinsic world that form the context of an individual's life), and the interactions between the two. This innovative model recently proposed by the World Health Organization has the potential to substantially modify the way in which clinical practice is currently conducted, shifting from disease-centered toward function-centered paradigms. By overcoming the multiple limitations affecting the construct of disease, this novel framework may allow the worldwide dissemination of a more proactive and function-based approach toward achieving optimal health status. In order to facilitate the translation of the current theoretical model into practice, it is important to identify the inner nature of its constituting constructs. In this article, we consider intrinsic capacity. Using the International Classification of Functioning, Disability and Health (ICF) framework as background and taking into account available evidence, five domains (i.e., locomotion, vitality, cognition, psychological, sensory) are identified as pivotal for capturing the individual's intrinsic capacity (and therefore also reserves) and, through this, pave the way for its objective measurement.