This work inevitably sprang out of our environmental biotechnology modules at the University of Durham, but it is not intended to be just another ‘book of the course’. Though it is clearly rooted in these origins, it reflects our wider, and rather varied, experiences of the field. In many respects, we have been fortunate; teaching has undoubtedly drawn on the ‘theory’, while our own consultancy has tended to focus us on the ‘application’.