Physics 321 is designed to provide a comprehensive introduction to the physics of the charged particle beams and modern particle accelerators. It is intended for students who will either pursue their research career in accelerator physics or use the high intensity beams, from charged particle beams, to synchrotron radiation, to FEL beams, generated by accelerators for their scientific research. This course will first give an introduction to various types of accelerators including electrostatic accelerators, induction linear accelerators, linear radio-frequency (RF) accelerators, and various circular accelerators such microtrons, cyclotrons, synchrotrons and storage rings. It will then focus on the basic accelerator and beam physics topics including, charged particle in electromagnetic fields, magnetic fields modeling, linear beam dynamics, charged particle beam optics, beam generation, confinement and guidance, and beam acceleration and phase stability. In addition, using modern storage rings as examples, this course will cover topics such as phase-space distributions and equilibrium sizes of the beam and beam life time issues. Using Duke free-electron laser (FEL) and High Intensity Gamma-Ray Source (HIGS) as examples, this course will also give an introduction to the physics of the FEL and laser-driven Compton gamma-ray source.