Dear colleagues and readers of our journal

Abstract

Dear colleagues and readers of our journal,

Last year there appeared one special issue of our journal, i.e., "Self-organization and collective behaviour in complex systems", alongside with three regular issues. This year we start with a special issue entitled "What is liquid?", in honour of Douglas Henderson, a member of our Editorial Board, dedicated to his 80th birthday. The collection of papers to appear in this issue is aimed at providing a critical review of the state of the art and of the open questions posed in the theory of liquids.