The most fundamental and complex problems in understanding climate and weather are our poor understanding of basic cloud properties and an inability to quantify the many effects cloud processes have on weather and climate. Models that predict such effects require accurate representations of cloud-particle processes (“microphysical” processes on the micron to centimetre scale) that in turn rely on hard-to-obtain in-situ observations of cloud particle sizes, shapes, phases and concentrations. Here, an overview of how aircraft cloud probes operate and what we learn from them about cloud microphysics is presented using data collected over the Southern Ocean and in tropical oceanic convective clouds. Data from these probes is advancing our understanding of cloud processes and is pointing to important next steps in representing clouds in weather and climate models. Exciting opportunities for future field work are discussed.