After pioneering work in the 1980s, plasma-based ion implantation (PBII) and plasma-based ion implantation and deposition (PBIID) can now be considered mature technologies for surface modification and thin film deposition. This review starts by looking at the historical development and recalling the basic ideas of PBII. Advantages and disadvantages are compared to conventional ion beam implantation and physical vapor deposition for PBII and PBIID, respectively, followed by a summary of the physics of sheath dynamics, plasma and pulse specifications, plasma diagnostics, and process modeling. The review moves on to technology considerations for plasma sources and process reactors. PBII surface modification and PBIID coatings are applied in a wide range of situations. They include the by-now traditional tribological applications of reducing wear and corrosion through the formation of hard, tough, smooth, low-friction, and chemically inert phases and coatings, e.g., for engine components. PBII has become viable for the formation of shallow junctions and other applications in microelectronics. More recently, the rapidly growing field of biomaterial synthesis makes use of PBII and PBIID to alter surfaces of or produce coatings on surgical implants and other biomedical devices. With limitations, also nonconducting materials such as plastic sheets can be treated. The major interest in PBII processing originates from its flexibility in ion energy (from a few electron volts up to about 100 keV), and the capability to efficiently treat, or deposit on, large areas, and (within limits) to process nonflat, three-dimensional workpieces, including forming and modifying metastable phases and nanostructures.