Anyone interested in acquiring this new book is likely to remember another book co-authored by G.V. Keller: Electrical Methods in Geophysical Prospecting (the second author was Frank C. Frischknecht). The high standard of the first book and its timeliness certainly helped it to become a classic in its field. It has already been reprinted several times. The prospective buyer of the new text will first be struck, however, by the exceedingly high price of the book, and then, as one leafs through it, by the inordinate amount of mathematics presented. The small potential market and the high cost of production may be invoked to explain the price, but a different, less highly mathematical approach would have reduced costs and widened the market, especially because the subject of magnetotellurics is now a topical one.