Quality by Design (QbD) is a systematic approach to pharmaceutical development that begins with predefined objectives and emphasizes product and process understanding based on sound science and quality risk management. Key aspects of QbD include establishing a Quality Target Product Profile (QTPP) that identifies critical quality attributes (CQAs), understanding critical material attributes (CMAs) and critical process parameters (CPPs), and implementing a control strategy for CQAs and CPPs. The ICH Q8 guideline introduced QbD, and it has been further developed through guidelines like ICH Q9 and Q10. Examples show how QbD has been applied scientifically in different pharmaceutical development and manufacturing processes.