The role of chemical reactions within the atmospheric multiphase system, i.e. aerosol particles and cloud droplets surrounded by a gas phase, has been recognized for several decades to affect the atmospheric composition. In this article, significant advancements in measurement techniques during the past 20 years are briefly described that led to the identification of thousands of organic compounds and molecular-scale processes within the atmospheric multiphase system. Similarly, the complexity of multiphase chemistry models has been increasing to include in detail the underlying chemical processes and phase transfers between gas, aqueous, and organic phases. The authors propose how complementary techniques, such as machine learning and molecular dynamics, can be used to constrain the resulting model complexity. They also identify chemical parameters to be further constrained in lab and field studies. Overall, the article highlights the need and future directions of increasingly interdisciplinary efforts to characterize the atmospheric multiphase chemistry system and its impacts on climate-chemistry interactions, atmospheric oxidation capacity and human health.