Advanced ultrafast amplifiers combine high power, excellent beam quality, and high repetition rates. Enormously high optical intensities, exceeding 10^16 W/cm^2, can be achieved by focusing such intense pulses in some medium. There are two typical amplification schemes, one using the Chirped Pulse Amplification (CPA) technique and another based on multi-pass pulse amplification through the amplification medium. Ultrafast amplifiers find applications where intense pulses for highly nonlinear processes, such as high harmonic generation, are required or for the acceleration of particles to high energies. They may be used in laser-induced nuclear fusion or for micromachining.