Purpose of the special issue: the idea for this issue arises from EGU General Assembly 2018 session TS11.5/GD10.5, "Understanding the unknowns: recognition, quantification, influence and minimisation of uncertainty in the geosciences". The rationale behind this proposal is to bring together a number of articles aimed at highlighting the importance of understanding uncertainty, often neglected by interpreters, geomodellers, and experimentalists, perhaps due to the societal expectation of a single (flawless) deterministic model and corresponding outputs. In this special issue, we hope to bring together geoscientists from a variety of fields interested in developing a more integrated understanding of how quantifying and recognising uncertainty in geological interpretation, models, and experiments broadens their applicability and increases their value.