The progress of carrier envelope phase (CEP) stabilization by the direct locking method developed at KAIST is summarized. The CEP of a femtosecond laser pulse has become a new laser parameter when the electric field of laser pulses, instead of the intensity, becomes a crucial interacting variable. The basic principle of the direct locking method is first explained, which operates in the time domain and generates CEP-stabilized laser pulses with identical CEP from a femtosecond oscillator. Then the method to achieve a long-term CEP stabilization, realized by installing a double feedback loop to a femtosecond laser, is explained. In addition the frequency-domain characteristics of the CEP-stabilized femtosecond laser are also analyzed. Finally the CEP stabilization of a kHz high-power femtosecond laser is presented. (C) 2012 Elsevier Ltd. All rights reserved.