There is a wave of renewed interest in the double layer structure in electrocatalysis, probably due to two reasons. First, a multitude of electrolyte effects, such as the cation effect and the pH effect , emerge recently in electrocatalysis, and there is growing consensus that demystifying these electrolyte effects requires fundamental knowledge of the double layer structure. Several review articles on electrolyte effects in electrocatalysis have been published recently. Second, a growing body of experimental data related to the double layer structure of single crystals of transition metals, notably platinum, have been reported recently. These new data, though not fully consistent with each other as detailed below, have already surprised us as they do not agree, even qualitatively, with classical double layer models.