Powder technology is a rapidly expanding technology and nowhere more than in particle characterization. There has been an explosion of new particle measuring techniques in the past ten year particularly in the field of on-line measurement. One of the main aims of this book is to bring the reader up-to-date with current practices. One important area of interest is the improvements in on-line light scattering instruments and the introduction of ultrasonic on-line devices. Another is the introduction of on-line microscopy, which permits shape analysis in conjunction with particle sizing. Schools of powder technology are common in Europe and Japan but the importance of this subject has only recently been recognised in America with the emergence of the Particle Research Centre (PERC) at the University of Florida in Gainsville.