Nature is full of struggle, as predicted by the theory of evolution through natural selection, yet there are also paramount examples where individuals help each other. These instances of helping have been difficult to reconcile with Darwin’s theory because it is not always obvious how individuals are working for their own direct benefit. Consequently, initial publications that offered solutions to subsets of the observed cases of helping, such as kin selection (Hamilton, 1964) or reciprocity (Axelrod & Hamilton, 1981; Trivers, 1971), are among the most influential and most cited papers in evolution / behavioural ecology. Despite these initial successes, models are often difficult to map on to actions, and empirical evidence for many proposed solutions is quite sparse. However, during the last few years, a wave of new studies and concepts has considerably advanced our understanding of the conditions under which individuals are selected to help others. We therefore think it is timely to bring together the state of the art concerning our knowledge of helping. Perhaps more importantly, reviewing our current knowledge should help us to identify the many gaps that still exist in our understanding of helping behaviour.