The intracellular signalling pathways that control cell function have been and still are, one of the most intensively studied aspects of biology. The aim of this work is to provide full reproductions of a set of key papers which have been chosen as landmark papers in the various aspects of intracellular signalling. The papers are accompanied by commentaries that describe why they are significant, how the work came about and summarize the advances that have been made up to the present time as a consequence of the original paper. The commentaries should also serve as reviews of aspects of cell regulation and may be read on their own.