This 47th volume of Reviews in Mineralogy and Geochemistry succeeds admirably at the very difficult task of summarizing, in a succinct and approachable manner, what is and is not known about noble gases and their roles in geochemistry and cosmochemistry. The list of significant contributions to our understanding of stellar and nebular processes, planetary and lunar science, and geoscience is long and diverse. Noble gases introduced the first evidence for isotopic heterogeneity in the solar nebula, and the presence of live but now extinct radionuclides, the latter leading to a fine-scale chronology of nebular processes and planetary evolution and the first estimates of the age of the elements in the universe. Noble gases have been instrumental in identifying and isolating relict nova and supernova grains, providing a unique insight into stellar nucleosynthesis and chemistry. Additional contributions include evidence for temporal changes in the composition of the solar wind, planetary and lunar cratering histories and time scales, evidence for pre-compaction irradiation of meteoritic material, constraints on processes and time scales of planetary degassing, atmosphere formation, and crust-mantle-core evolution.