The changing development paradigm resulting from the US Food and Drug Administration’s quality-by-design (QbD) initiative and International Conference on Harmonisation (ICH) guidelines requires increased process understanding of the drug substance and drug product throughout development and manufacturing. A lack of information can result in delays in regulatory approval and higher costs. Applying QbD principles leads to greater process understanding, facilitates regulatory approval and streamlines postapproval changes. Case studies on the manufacture of a bulk powder and the development of a tablet show the application of QbD principles, including defining critical quality attributes, implementing risk assessment, optimising process development, developing a design space and performing a criticality analysis.