Single neurons are the fundamental constituents of all nervous systems. Understanding the properties and dynamics of single neurons is therefore one of the key challenges in modern neuroscience. Since the work of Lapicque (1907) [see also the recent translation by Brunel and van Rossum (2007)], single neuron models have enjoyed great popularity and have been the subject of many theoretical studies. Two broad categories of spiking neuron models have been extensively studied and used: Hodgkin-Huxley-type neuron models and simplified phenomenological neuron models, of which the integrate-and-fire model is the most famous representative. Each model type presents its own set of advantages and drawbacks. The Hodgkin-Huxley framework permits the design of detailed, biophysically realistic models, which can be used to study the effects of different types of ion channels including their distribution along dendrites. However, these models are computationally expensive and their analysis is usually difficult. Simple phenomenological neuron models, on the other hand, are analytically tractable and computationally cheap, but their realism is questionable. Both types of models have been used in countless studies of single neurons and network models, with the ultimate aim of understanding how information processing in single neurons and neural circuits gives rise to behaviour.Despite the tremendous popularity both types of models enjoy, the question of their quantitative accuracy in reproducing experimentally measured neuronal dynamics has been barely addressed until recently. It was implicitly assumed that Hodgkin-Huxley-type neuron models are the most realistic, while simplified phenomenological neuron models were overlooked in that regard but extensively used because of their simplicity. However, are either of these models able to predict the rate and timing of output spikes of a real neuron, given arbitrary patterns of synaptic input? Can they correctly predict the result of the interactions between dendrites and soma? And can they quantitatively predict the effect of various intrinsic neuronal mechanisms, for example those underlying adaptation or bursting? With recent initiatives such as the Blue Brain Project (Markram 2006) or the recent large-scale model by Izhikevich and Edelman (2008), it is now time to try to answer these questions. In order to provide the community with a benchmark to address these questions, we set up an international scholarly challenge on quantitative single neuron modeling 1 . The present Special Issue comprises a selection of papers that address precisely these questions, and extensively describe the challenge: can Hodgkin-Huxley-type neuron models or simplified phenomenological neuron models predict the activity of real neurons? What is the minimal level of description required to achieve a reasonable accuracy of predictions made by 1