This Festschrift is published in honor of Yuri Gurevich's 80th birthday. An associated conference, YuriFest 2020, was planned for May 18-20 in Fontainebleau, France, in combination with the 39th Journees sur les Arithmetiques Faibles also celebrating Yuri's 80th birthday. Because of the coronavirus situation, the conference had to be postponed, but this Festschrift is being published as originally planned. It addresses a very wide variety of topics, but by no means all of the fields of logic and computation in which Yuri has made important progress.

This Festschrift is published in honor of Yuri Gurevich's 75th birthday. Yuri Gurevich has made fundamental contributions on the broad spectrum of logic and computer science, including decision procedures, the monadic theory of order, abstract state machines, formal methods, foundations of computer science, security, and much more. Many of these areas are reflected in the 20 articles in this Festschrift and in the presentations at the "Yurifest" symposium, which was held in Berlin, Germany, on September 11 and 12, 2015. The Yurifest symposium was co-located with the 24th EACSL Annual Conference on Computer Science Logic (CSL 2015).