AS readers of these columns will be aware, workers in the Radiation Laboratory of the Massachusetts Institute of Technology are producing a series of books on microwave techniques which, when complete, will contain twenty-eight volumes, one of which is to be an index of the whole series. Reviews of several books of the series have already appeared in Nature, and the present notice deals with a further six volumes, namely, numbers 9, 11, 14, 15, 16 and 23. Microwave Transmission Circuits Edited by George L. Ragan (Massachusetts Institute of Technology: Radiation Laboratory Series, No. 9.) Pp. xvii + 725. 51s. Technique of Microwave Measurements Edited by Assoc. Prof. Carol G. Montgomery. (Massachusetts Institute of Technology: Radiation Laboratory Series, No. 11.) Pp. xix + 939. 60s. Microwave Duplexers Edited by Louis D. Smullin Assoc. Prof. Carol G. Montgomery. (Massachusetts Institute of Technology: Radiation Laboratory Series, No. 14.) Pp. xiv + 437. 39s. Crystal Rectifiers Assoc. Prof. Henry C. Torrey Assoc. Prof. Charles A. Whitmer S. A. Goudsmit James L. Lawson Leon B. Linford Albert M. Stone. (Massachusetts Institute of Technology: Radiation Laboratory Series, No. 15.) Pp. xiii + 443. 36s. Microwave Mixers Robert V. Pound; with a Chapter by Eric Durand. Edited by C. G. Montgomery and D. D. Montgomery. (Massachusetts Institute of Technology: Radiation Laboratory Series, No. 16.) Pp. xii + 381. 33s. Microwave Receivers Edited by Assoc. Prof. S. N. Van Voorhis. (Massachusetts Institute of Technology: Radiation Laboratory Series, No. 23.) Pp. xviii + 618. 48s. (New York and London: McGraw-Hill Book Co., Inc., 1947–48.)