Ultrasonics International 91 is a documentation of conference proceedings that discusses the status and future of acoustic microscopy and its application to materials research, especially focusing on its quantitative analyses. Acoustic microscopy, using focused waves, has been receiving increased attention as a technology applicable to materials characterization at the microscopic scale. In acoustic microscopy, the excitation and propagation of leaky surface acoustic waves (LSAWs) in the environment of the coupling liquid at the solid specimens are observed. Three types of the systems have been developed: point-focus-beam (PFB), line-focus-beam (LFB), and directional PFB acoustic microscopes. In this paper, a brief history of the practical developments is first presented, followed by LFB acoustic microscopy for quantitative material characterization and some applications concerned with characterization of elastic anisotropy and inhomogeneity of electronic materials, such as LiNb03 and LiTa03 single crystals, and thin-film characterization. This book gives a comprehensive account of the majority of the oral and poster contributions made during the conference, and makes a valuable addition to a student or researchers' ultrasonic literature.