Techno-economic modeling has been a valuable tool in directing and assessing the research and development efforts for biomass-to-ethanol processes. In developing a techno-economic model of a "generic" wood-to-ethanol process, we decided to follow a three-pronged design approach. This initially consisted of a detailed review of the current definition and technical maturity of the process, which concluded that the process remains complex and immature. More recently, we have critically assessed/compared two inherited models, and examined the historical and current trends in modeling design. We confirmed that process complexity and immaturity, in association with the capabilities of the available modeling tools and the ease with which they can be used, influenced the design and implementation of past models. We have discussed these influences with reference to our own model development decisions. For example, on review of two inherited techno-economic models, we decided that our new model would require a greater degree of flexibility in its structure and user interface.