The 30 years since the first appearance of this book have seen a revolution in biology and the impact on entomology has been enormous. In writing the first edition, I tried to approach the insect as a whole organism and to combine functional morphology with physiology. That is still my aim in this rewriting, but the growth of biological science has required me continually to make decisions about where to draw the line. In particular, I felt it was impossible for me to do justice to molecular studies. I made this decision reluctantly, because molecular biology is so obviously a key to our understanding of how insects work, and I do make some reference to molecular work, especially where it causes us to rethink older ideas.

I believe it is critically important to produce a synthesis in a single volume. This is essential for the students of entomology for whom the book was, and is, primarily intended. I hope, also, to provide a useful reference for biologists in other fields who use insects as models, but I want to encourage them to think of the insect as a whole. Where does their system belong in the functioning of the organism? Systems in isolation sometimes don't make much sense.

While I have retained the major divisions that I used in the earlier editions, I have combined some chapters and rearranged them to some extent. I have adopted American spellings throughout.