This book contains essays on data integrity. Data integrity is the most basic element of work in any scientific discipline. Nothing of lasting value in the hard sciences (physics, chemistry, biology, astronomy, et al.) lacks integrity in the data used to support the premises, the logical arguments proposed, and the conclusions drawn. The point of validation is, after all, to ensure that all results obtained and reported are true. The original premise of our book was to merge the global standard for pharmaceutical analytical methods for regulatory applications [ICH Q2(R1)] with contemporary thinking on ensuring data quality by thoroughly understanding a method and its intended application (QbD). During a preproduction meeting, an incisive question led to expanding the scope of the original five chapters: "Can this be applied to fields other than pharmaceuticals?" The answer was: Yes. Three chapters were added to explore the applications of Quality by Design theory to real world problems that are bound not only by regulations, but by business constraints, professional ethics, time, resources, and technology. They may serve as case studies for classes of advanced students. The scientific approach is rigorous, drawing on, and integrating, classical wet and modern instrumental analytical chemistry knowledge. The reasoning is detailed and well-documented. Examples are carefully explained. Two are based on historical events. The other is a problem that is not yet fully resolved despite its importance and significant risks to human health globally. The tone throughout is conversational. It is intended to involve students - and any reader who has a vested interest in data integrity, which includes the global scientific communities from academia, industry, and government, and producers and consumers of quantitative measurements and the goods and services obtained by their use. The objective is to impart an intuitive understanding of method validation: planning, execution, and documentation, with examples of practices and problems, and with practical strategies for addressing both. A special feature is the inclusion of "Hints" - brief comments offering experience-based advice acquired while developing, validating, reviewing, and auditing analytical methods (and data) in a variety of industries and countries.