Dynamics is a text aimed at graduate students and advanced undergraduates in astronomy and physics; its scope is appropriate to a one-semester course. Its coverage of celestial dynamics includes a discussion of three-body effects, resonances, and chaos. The section on stellar dynamics covers potentials, orbits, collisionless stellar systems, and collisional effects such as dynamical friction and relaxation. Its final section on gas dynamics discusses topics such as turbulence, gas accretion (including accretion disks) and gas outflow (including winds and jets). Dynamics is part of the Ohio State Graduate Astrophysics Series, in which emphasis is placed on order-of-magnitude calculations and the development of physical insight.