Fundamentals of microwave ion sources used for ion implantation as well as their main features are reviewed and evaluated. Ion sources using plasmas generated by microwave discharge in a magnetic field have many advantageous features. Since they operate even with reactive source materials, they can provide long-life stable ion beams for a variety of ion species. They can provide either multiply-charged ion beams or high-current ion beams of singly-charged ions depending on selected operational conditions. High-current beams of singly-charged ions can be extracted in various sizes and forms. An ion source that extracts an ion beam of 40 mm diameter through a multiaperture lens can provide argon, hydrogen and oxygen ion beams of several hundred mA at 5 kV. The ion current can be further increased by increasing the volume of the discharge chamber and the area of the multiaperture lens. An ion source that extracts a slit-shaped beam suitable for ion implantation can provide mass-separated currents of 10 mA (maximum 15 mA) for As + and P + as well as various metal ions of several mA. Due to versatility of beam extraction, this ion source has been modified to a higher voltage (120 kV) by combining a double-stage extraction lens, and to a higher mass-separated current (30 mA) by lengthening the ion exit slit.