Philosophers of science frequently bemoan (or cheer) the fact that today, with the supposed collapse of logical empiricism, there are now ;;10 grand systems. However, although this mayor may not be true, and if true mayor may not be a cause for delight, no one should conclude that the philosophy of science has ground to a halt, its problems exhausted and its practioners dispirited. In fact, in this post­ Kuhnian age the subject has never been more alive, as we work with enthusiasm on special topics, historical and conceptual. And no topic has grown and thrived quite like the philosophy of biology, which now has many students in the field producing high-quality articles and monographs. The success of this subject is due above all to the work and influence of one man: David Hull. In his own writings and in the support he has given to others, he has shown true leadership, in the best Platonic sense. It is now twenty years since Hull fnt gave his seminal paper 'What the philosophy of biology is not', and to mark that point and to show our respect, gratitude and affection to its author, a number of us who owe much to Hull decided to produce a volume of essays on and around themes to which Hull has spoken.