The idea to collate and edit a book on virus evolution occurred to each of us quite independently, but when we discovered that we had this common desire, it seemed reasonable to pool our resources, experiences, and energies. We assumed that, whereas none of us had a firm grasp of either the questions or the answers, collectively we might be able to attract as participants many people who have given virus evolution more than passing thoughts. Further, we did not want to edit a book containing ‘great thoughts by great people’. From the outset, we wanted to bring together current data-based views of the evolution of various viruses. Considering that thousands of viruses have been recognized, it was an obvious impossibility to try to cover the entire field. Indeed, we have made a concerted effort not to do so. Keeping in mind Duncan McGeoch's dictum that ‘Viruses may be looked on as mistletoe on the Tree of Life’, we fully expected that evolutionary practice would vary, and vary considerably from one family to another.

Therefore, we thought it appropriate to convene a meeting of people we expected would provide a basis for organizing a book on the subject and who might provide at least a glimmer of a consensus. We organized a symposium ‘Co-evolution of viruses, their hosts and vectors’ in Madrid from December 9–11, 1991, and invited some of the colleagues we knew to be working directly or indirectly on virus evolution, and advertisements attracted others who wished to join us.