The paper reviews and compares various atmospheric-pressure plasma sources, including transferred arcs, plasma torches, corona discharges, dielectric barrier discharges, and the recently developed atmospheric-pressure plasma jet. Traditional sources like arcs and torches have high electron and neutral temperatures (over 3000°C) and high charge species densities (10^10–10^15 cm^-3), making them suitable for metallurgy. Corona and dielectric barrier discharges produce non-equilibrium plasmas with lower gas temperatures (50–400°C) and typical charged species densities of weakly ionized gases, but their non-uniform nature limits their use in materials processing. The atmospheric-pressure plasma jet, on the other hand, exhibits characteristics similar to conventional low-pressure glow discharges, with gas temperatures ranging from 25–200°C, charged-particle densities of 10^11–10^12 cm^-3, and high concentrations of reactive species (10–100 ppm). This source can be scaled to treat large areas, making it suitable for applications previously restricted to vacuum systems. The paper discusses the physics and chemistry of these plasma sources, including current-voltage characteristics, electron and neutral temperatures, charged particle densities, and gas compositions. It also provides a quantitative comparison between traditional sources and the atmospheric-pressure plasma jet, highlighting the plasma jet's potential for a wide range of materials applications.The paper reviews and compares various atmospheric-pressure plasma sources, including transferred arcs, plasma torches, corona discharges, dielectric barrier discharges, and the recently developed atmospheric-pressure plasma jet. Traditional sources like arcs and torches have high electron and neutral temperatures (over 3000°C) and high charge species densities (10^10–10^15 cm^-3), making them suitable for metallurgy. Corona and dielectric barrier discharges produce non-equilibrium plasmas with lower gas temperatures (50–400°C) and typical charged species densities of weakly ionized gases, but their non-uniform nature limits their use in materials processing. The atmospheric-pressure plasma jet, on the other hand, exhibits characteristics similar to conventional low-pressure glow discharges, with gas temperatures ranging from 25–200°C, charged-particle densities of 10^11–10^12 cm^-3, and high concentrations of reactive species (10–100 ppm). This source can be scaled to treat large areas, making it suitable for applications previously restricted to vacuum systems. The paper discusses the physics and chemistry of these plasma sources, including current-voltage characteristics, electron and neutral temperatures, charged particle densities, and gas compositions. It also provides a quantitative comparison between traditional sources and the atmospheric-pressure plasma jet, highlighting the plasma jet's potential for a wide range of materials applications.