Dear colleagues!

This special issue, supported by the grant of the Belarusian Foundation for Fundamental Research, presents the selected papers of two conferences held in Minsk this year. The first event was the 25th International Seminar "Nonlinear Phenomena in Complex Systems", 21-25 May 2018 , the meeting that twenty years ago gave rise to the foundation of our Journal. The second event was joint meeting XIX International Conference School "Foundations & Advances in Nonlinear Science"and IV International Symposium "Advances in Nonlinear Photonics", September, 24 - 28, 2018. Both events gathered participants from all over the world including Russia, Germany, France, Canada, Sweden, Portugal, Poland, Lithuania, Romania, Slovakia and Belarus. The topics of the Conferences have involved theoretical and applied aspects of self-organization and nonlinear dynamics characteristic for complex systems. The distinguishing feature of the scientific subjects discussed during these events was their interdisciplinary character.

The papers collected in this issue cover research trends nonlinear optical phenomena and laser dynamics, nanomaterials, nanophotonics and nanotechnology, novel materials, extreme and relativistic nonlinear optics, high energy physics, quantum chemistry and dynamical system theory. We hope that this special issue may be useful for the members of scientific community, providing new information about modern trends in the interdisciplinary research activities realized all over the world.

Organizing Committee of the NPCS 2018, FANS & ANPh 2018 meetings and Editorial Board of the NPCS Journal.