This book reviews recent advances in experimental and theoretical understanding of phenomena on the picosecond and femtosecond time scales. The technology and applications in this field have shown remarkable progress recently. It is now possible to produce and measure pulses much shorter than 10 fs, which is approaching the inherent limit, in the visible region. Improvements in wavelength range, power levels and other performance parameters are also reported. These high-performance light sources are being used to study ultrafast phenomena in physical, chemical and biological systems and in artificial devices. The recent results reported and reviewed in this book provide a picture of the current status of the field.