A metabolic network is the complete set of metabolic and physical processes that determine the physiological

Physiology

Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

 and biochemical

Biochemistry

Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...

properties of a cell. As such, these networks comprise the chemical reactions of metabolism as well as the regulatory interactions that guide these reactions.

With the sequencing of complete genomes, it is now possible to reconstruct the network of biochemical reactions in many organisms, from bacteria to human. Several of these networks are available online:
Kyoto Encyclopedia of Genes and Genomes (KEGG)http://www.genome.ad.jp, EcoCyc http://www.ecocyc.org, BioCyc http://biocyc.org and metaTIGER http://www.bioinformatics.leeds.ac.uk/metatiger/.
Metabolic networks are powerful tools, for studying and modelling metabolism.