The investigation of cellular metabolic pathway networks is a remarkably varied field requiring a wide range of knowledge and theoretical and experimental tools taken from a diversity of scientific disciplines. This diversity, from basic to applied science, and involving mathematical modeling to experimental approaches, is well illustrated by the articles in this theme issue of Molecular BioSystems. 

The articles described in this issue involve a systems approach to the study of metabolism in bacteria supported by comprehensive measurements made possible by the new technologies and theoretical and mathematical analyses which constitute the field now known as Systems Biology. 

The issue is introduced by Professors Hirotada Mori from Nara University in Japan and Tadhg Begley from Cornell University in the USA. Both are members of the Molecular BioSystems Editorial Board.