Metabolic networks supply the precursors, energy and reducing power required for the synthesis and turnover of cellular components. The associated flows of material – the metabolic fluxes – are crucial in determining the performance and productivity of cells and organisms. For example, in an agricultural context, the production of harvestable end-products of plant metabolism is entirely dependent on the flux phenotype of the plant; while in biotechnology, the exploitation of micro-organisms and plants hinges on an ability to reconfigure the metabolic network to favour a flux distribution that leads to the preferential synthesis of particular products. Thus the fluxes supported by the plant metabolic network play a pivotal role in determining both phenotype and productivity. My main interest lies in understanding the organisation and regulation of the metabolic fluxes that occur in the plant metabolic network. A knowledge of the transcriptome, proteome or metabolome does not lead easily to the metabolic flux phenotype, and internal fluxes within the metabolic network have to be deduced from a suite of computational and experimental tools. My research group is strongly involved in the development and application of steady-state metabolic flux analysis (MFA), a technique that allows fluxes to be deduced from a stoichiometric model of the network using stable isotope (13C) labelling data and measurements of biosynthetic outputs. We complement this MFA work with an in silico approach using genome-scale models and constraints-based flux balance analysis. Together these methods allow us to assess the metabolic phenotypes of wild type, mutant and transgenic plants, and thus the metabolic impact of genetic and environmental perturbations.