It is a great pleasure that we are now publishing the fourth volume of the series on PUILS, through which we have been introducing the progress in ultrafast intense laser science, the frontiers of which are rapidly expanding, thanks to the progress in ultrashort and high-power laser technologies. The interdisciplinary nature of this research ?eld is attracting researchers with di?erent expertise and backgrounds. As in the previousvolumeson PUILS, each chapter in the presentvolume, which is in the range of 15-25 pages, begins with an introduction in which a clear and concise account of the signi?cance of the topic is given, followed by a description of the authors' most recent research results. All the chapters are peer-reviewed. The articles of this fourth volume cover a diverse range of the interdisciplinary research ?eld, and the topics may be grouped into four categories: strong ?eld ionization of atoms (Chaps. 1-2), excitation, ioni- tion and fragmentation of molecules (Chaps. 3-5), nonlinear intense optical phenomena and attosecond pulses (Chaps. 6-8), and laser solid interactions and photoemissions (Chaps. 9-11).

1. A gauge-invariant theory of intense-field Coulomb approximations to all orders.- 2. Strong-field photoionization by few-cycle laser pulses.- 3. Wavepacket Dynamics of Molecules in Intense Laser Fields.- 4. Molecular ion beams interrogated with ultrashort intense laser pulses.- 5. Dynamical Reaction Theory for Vibrationally Highly Excited Molecules.- 6. Relativistic quantum dynamics in intense laser fields.- 7. Attosecond scale multi-XUV-photon processes.- 8. Ultrashort pulse collapse in quadratic media.- 9. Femtosecond laser induced various luminescent phenomena in solid materials.- 10. Prospect of Laser-Driven X-Ray Lasers for Extension to Shorter Wavelengths.- 11. Femtosecond Laser Applications in Micro/Nano Science and Technology-Nonlinear Effects in Photonic Crystal Fibers, Femtosecond Laser-induced Forward Transfer, and Femtosecond Laser Manipulation System for Biology.