Book excerpt: The book highlights the current practices and future trends in structural characterization of impurities and degradants. It begins with an overview of mass spectrometry techniques as related to the analysis of impurities and degradants, followed by studies involving characterization of process related impurities (including potential genotoxic impurities), and excipient related impurities in formulated products. Both general practitioners in pharmaceutical research and specialists in analytical chemistry field will benefit from this book that will detail step-by-step approaches and new strategies to solve challenging problems related to pharmaceutical research.