This book presents selected contributions from ICMFM XX and the Polish National Conference—KKMP.  The XX International Colloquium on Mechanical Fatigue of Metals (ICMFM XX) was organized on 15–17 September 2021, in the Faculty of Mechanical Engineering of the Wroclaw University of Science and Technology, in Wrocław City, Poland, in a remote form. Its aim was to facilitate and encourage the exchange of knowledge and experiences among the different communities involved in both basic and applied research in the field of fatigue of metals, looking at the problem of fatigue from a multiscale perspective, and exploring analytical and numerical simulative approaches, without losing the perspectives of the application. The Polish National Conference—KKMP 2021—was organized remotely with 50–80 prominent international participants from the fracture mechanics community. 

This book contains full papers presented at the First Virtual Conference on Mechanical Fatigue (VCMF 2020), which was organised by the University of Porto (FEUP, Portugal), the Wroclaw University of Science and Technology (Poland), University of Electronic Science and Technology of China (China), Siberian Federal University (Russia), and the ESIS/TC12 Technical Committee (European Structural Integrity Society–ESIS), between 9 and 11 of September 2020. This conference was intended to be a forum of discussion of new research concepts, equipment, technology, materials and structures and other scientific advances within the field of mechanical fatigue and fracture. The first edition of the VCMF 2020 event has reached more than 60 participants from more than 20 nationalities demonstrating the vitality of this new event.