A rational approach to biotransformation process design can result in significantly reduced optimisation and scale-up times. This thesis describes the application of a structured approach to bioreactor selection for transketolase catalysed biotransformations. A decision making procedure based initially on characterisation of the reaction components, the biocatalyst, the reaction and the interactions between them was employed. These characteristics were used to set constraints and reactor options could then be evaluated in terms of relative performance within these constraints. The identification of the key parameters and constraints on transketolase biocatalysis was conducted employing a model reaction as the research tool. Analytical methodologies were developed for the model reaction and utilised for biotransformation characterisation studies. These characteristics enabled tentative definition of the key constraints of the process and suitable reactor options for further evaluation. A number of the reactor options were investigated. Validation of the constraining parameters determined from these initial studies was conducted using a second reaction. Research involved the development of the analytical methods for this validation reaction, investigation of the key parameters perceived as constraints and a theoretical evaluation of the reactor options. The constraints of transketolase-catalysed biotransformation processes utilising substrates exhibiting a range of industrially representative characteristics has therefore been defined. Based on this information the optimum reactor configurations for a range of transketolase catalysed biotransformations can be assigned based on the acquisition of a small but definitive set of data. The application of this type of approach to industry has been considered.