Francisco Varela (1946-2001):: Filling the mind - brain gap: A life adventure

One of the most eminent neuroscientists recently passed away in Paris. Professor Francisco Varela was a scholar that approached science with a remarkably broad and integrative perspective, deeply contributing to a diversity of fields, from mathematics to epistemology, from immunology to neuroscience. He was strongly influenced by Buddhism and actively participated in unraveling the relationship between science and spirituality. This article introduces a special edition of Biological Research dedicated to the memory of this great man. It contains a collection of valuable contributions by various authors who collaborated with Varela at different moments of his outstanding scientific career. Their articles cover most of the fields in which he made contributions.