This monograph comprises three chapters, each concerning a different aspect of deuterium. Chapter One discusses in detail the factors governing whether deuteration strategies will give rise to a deuterium KIE (kinetic isotope effect), which has many beneficial effects including increased drug resistance to metabolism, which is particularly important in radiopharmaceutical sciences. Chapter Two describes the properties of Deuterium Oxide (D2O), an isotopic form of water which contains two atoms of deuterium and one atom of oxygen, specifically its characteristic shielding action against external stress agents. Chapter Three presents the T-c-state diagram of the Pd-D system and proposes the crystal structure of ß- and ų- phases.