Femtosecond lasers have opened up new avenues in materials processing due to their unique features of ultrashort pulse width and extremely high peak intensity. One of the most important aspects of femtosecond laser processing is that strong absorption can be induced even in materials that are transparent to the femtosecond laser beam, thanks to nonlinear multiphoton absorption. This multiphoton absorption allows for not only surface processing but also three-dimensional internal microfabrication of transparent materials such as glass. This capability enables the direct fabrication of three-dimensional microfluidics, micromechanics, microelectronics, and microoptics embedded in the glass. Furthermore, these microcomponents can be easily integrated into a single glass microchip through a simple procedure using the femtosecond laser. Thus, femtosecond laser processing offers significant advantages.