This textbook uses the properties of planetary systems, including own Solar System, to illustrate the rich variety of behavior permitted by Newton's law of gravity. The textbook then expands its view to examine stellar dynamics - the study of systems containing a very large number of stars or other celestial bodies. The different techniques used for celestial dynamics and stellar dynamics are compared and contrasted. However, throughout the text, emphasis is placed on the underlying physics that applies on scales as small as the Earth - Moon system and as large as a cluster of galaxies.