The physiology and pathophysiology of the ME viewed from its ventilation and pressure regulation both by the ET and TMGE are described in this book. This is one of the main research projects in which our department has been involved for several years. Although, as a matter of course, this is still far from a perfect job, I believe that several new findings that would not had been discovered had we only paid attention to the ET were obtained through these studies, and I sincerely hope that these findings are useful in the daily clinical practice of otology. The studies described herein have found that a well-pneumatized mastoid is important for ME ventilation and pressure regulation, and that mastoidectomy not only deprives the mastoid of this important physiological function but also probably causes postoperative recurrent cholesteatoma. It is therefore suggested that the mode of ME surgery should be carefully selected in line with the surgical intervention to the mastoid, and that irreversible and organic impairment of the TMGE function in the mastoid, as well as the ET function, are closely related to the pathogenesis of cholesteatoma, which is the worst sequelae of OME in children. Although I feel it is necessary to further clarify the pathogenesis of ME inflammatory diseases in order to develop new treatments on the basis of these findings, I believe this book will be useful for otologists in their daily clinical practice.