The installation of piles by vibratory methods is discussed and illustrated by case histories. The influence of vibration frequency - which can be controlled during vibratory driving but not during impact driving - on pile penetration, bearing capacity and emission of vibration is examined. The driving process affects the performance of vibratory-driven piles more strongly than impact-driven piles. Concepts are presented for assessing driveability. The importance of resonance of the vibrator-pile-soil system (system resonance) for driveability and pile bearing capacity is explained. Ground vibrations measured on and below the ground surface show that strong oscillating horizontal stresses are generated. These stresses can temporarily reduce the shaft resistance during driving, which can explain why vibratory driving is effective even in dense granular soils. Model tests show that, in granular soils, the bearing capacity of piles vibrated after driving at system resonance is significantly higher than that of piles installed only at high frequency. A concept is described suggesting that, during vibratory driving at high frequency, a zone is created adjacent to the pile shaft where the normal effective stress acting against the pile shaft is reduced due to arching. This arching effect can explain the reduced shaft resistance of piles installed at high frequency.