This is an outward facing book for people who need to understand Geophysics because it can solve the problems they regularly encounter and help to deliver their optimal geotechnical solution, proved by the essential, but last to be applied, intrusive investigation. It may, of course, be of significant use to students and geophysical practitioners as it contains a wealth of case studies kindly provided by friends, colleagues and collaborators.The people to whom this book is addressed do not require a great understanding of the mathematical basis of geophysics but do need to understand the physical principles, what information can be gleaned, the limitations and boundaries of interpretation and especially how we can combine techniques in an integrated way to solve subtle, complex and critical problems which one technique alone cannot solve.