I see a man's life is a tedious one. Cymbeline, Act III, Sc. 6. It is well known that the best way to learn a subject is to teach it! Along the same lines one might also say that a pleasant way of learning a subject and at the same time getting to know quite a few of the workers active in it, is to arrange and to attend an Advanced Study Institute (ASI) or a workshop lasting about two weeks. This was and is the wisdom behind the NA TO-ASI programme and much as people fear that a fortnight may be too long, before it is over everyone feels that it was too short, especially if the weather had cooperated. Organising this ASI which resulted in this volume has been a very good learning experience. I started my career in research with invertebrates and retained an interest in them over the years due to my teaching a course and working sporadically on various aspects of photoreception in Polychaetes, Crustaceans and Insects. Thus, the thought of organising an ASI on photoreception and vision in invertebrates had been brewing in my mind for the past half a dozen years or so. It was felt that it will be desirable to do a bit of stock taking and discuss possible new approaches to the study of this matter.