This presentation will describe a multi-scale modeling approach to predict the processing and mechanical behaviour of textile composites, including effects of materials and process variability. Based around the TexGen textile modeling schema, this will consider the micro-scale fibre arrangement and meso-scale variability in yarn paths and ply nesting. Modelling tools for laminated polymer composites are now fairly mature and designers can perform structural analyses for composites built up from unidirectional prepreg using laminate theory and finite element analysis. Composites based on textile reinforcements can also be analysed using similar techniques with limited accuracy. Simulations of the manufacturing process are also reasonably advanced, and commercial simulation tools exist for resin flow and cure. A key requirement for resin flow modelling is accurate permeability data for the reinforcement, which are usually determined experimentally although predictive models do exist for simple fibre arrangements. There is now a gr owing interest in the use of such tools to predict the occurrence and consequences of defects such as meso/ macro-scale voidage, although to date only relatively crude simulation approaches to this problem have been presented. Fundamental modelling techniques for textile composites are less advanced in terms of industrial usage: traditional 'laminate' based methods are limited, and unable to determine the effect of fibre architecture on mechanical and processing behaviour. Several groups have demonstrated the use of unit-cell models to provide this fundamental modeling capability. However these focus largely on idealized textile structures, ignoring the variability that can exist at all length scales. This variability largely explains the scatter in measured processing and mechanical behavior. In this paper, a multi-scale modelling approach will be described, within which models at the micro-, meso-, and macro-scales are connected to provide a fully predictive approach. These are based in particular around the TexGen open source textile modelling schema, which can generate geometric models for arbitrary textile reinforcements, from which composites processing and mechanical properties can be predicted. Here this approach will be utilized to study variability in fibre arrangement at the micro-, meso- and macro-scales and the effects of such variability on permeability, resin flow and composite mechanical properties. Specifically this will include the effects of random fibre packing at the micro-scale and variable yarn paths and ply nesting at the meso- and macro-scales.