1.1   The purpose of this guide is to establish a framework and context for process understanding for pharmaceutical manufacturing using the principles of quality by design (QbD) (Juran, 1992;2 ICH Q8). The framework is applicable to both drug substance (DS) and drug product (DP) manufacturing. High (detailed) level process understanding can be used to facilitate production of product which consistently meets required specifications. It can also play a key role in continual process improvement efforts.