The world in which we live is characterised by spatial and temporal hierarchies. Mesoscience provides a unified approach to explain scientific, technical and societal problems that enjoy the common characteristic of possessing an inherent multi-scale hierarchal nature. Mesoscience relies on a modus operandi based on the identification of competing mechanisms; through new mathematical frameworks and physical observations it devises the dominant mechanisms which ultimately regulate the behaviour of complex systems. Mesoscience provides the vision to bridge the gap between “small” and “large” scales (at any level of the hierarchy) by elucidating the science and the mathematics regulating the “in-between” behaviour.