Quality by Design (QbD) is currently receiving increased attention from the pharmaceutical community. As a result, most major biotech manufacturers are in varying stages of implementing QbD. Here, I present a case study that illustrates the step-by-step development using QbD of a purification process for the production of a biosimilar product: granulocyte colony-stimulating factor (GCSF). I also highlight and discuss the advantages that QbD-based process development offers over traditional approaches. The case study is intended to help those who wish to implement QbD towards the development and commercialization of biotech products.