Droplet-surface interactions are fundamental in a plethora of critical phenomena. These range from designed engineered process, like, for example, spray coating or spray cooling, to those processes that occur naturally such as infrastructure fouling from rain, and the deposition and evaporation of pathogen containing human sputum droplets on surfaces. While we have empirical correlations for most single droplet heat transfer and evaporation process, such correlations remain elusive when the process occurs on complex surfaces, due to the sheer number of variables that need to be considered. These include surface roughness, the height and shape of the features, the size of the features relative to the droplets, the liquid surface energy (or wettability) and the difference between the surface temperature and the liquid saturation temperature. Sprays are significantly more complicated due to droplet/droplet interactions, liquid films, and polydispersity. In this presentation I will outline the status of our understanding, unpack some of the unsolved issues, including relevance to real world applications. I will explain the experimental that work that we have been working on. I will particularly focus on the role of surfaces on the droplet dynamics, from fundamental single droplet impingement to multiple droplets, and all the way to spray impingement. Single droplet impingement is a necessary starting point in the understanding of spray impingement, but it is not a realistic model for the spray process that includes droplets of different sizes, moving at different velocities and possibly at different directions, and that impact surfaces that may be partially wetted. I will make recommendations as to what research is needed to be able to optimise the heat flux from sprays. As spray cooling offers the highest heat transfer rate of any convective process, it will be needed for future ultra-high-flux cooling applications. Systems with requirements for particularly high heat transfer are coming to the fore in power electronics as we transition towards electrifying our energy supply. Finally, I will discuss how surface hydrophobicity inherently effects the evaporation rate of small droplets, and the effect this may have on surface borne pathogen spread.