Atmospheric aerosols (small airborne particles) present an exciting scientific puzzle: they come in a variety of shapes and species and interact in complicated ways with each other and the rest of the climate system. Consequently, it is challenging both to observe and model them. Yet aerosols affect the planet in many important ways: they modify the amount of global warming due to greenhouse gases, they represent a health hazard for humans and a nutrient source for the biosphere. This talk will consist of two parts: an introduction to aerosol science and an overview of work on uncertainties in aerosol modelling.