The deep mixing method (DM) developed in Japan and Sweden in the 1970s has gained popularity worldwide. The DM-improved ground is a composite system comprising stiff stabilized soil and un-stabilized soft soil, which necessitates geotechnical engineers to fully understand the interaction of stabilized and un-stabilized soils and the engineering characteristics of in-situ stabilized soil. The success of the DM project cannot be achieved by the well determined geotechnical design alone but is guaranteed only when the quality and geometric layout envisaged in the design is realized in the field with an acceptable level of accuracy. The process design, production with careful quality control and quality assurance are the key issues in the DM project. This book is intended to provide the state of the art and practice of quality control and assurance on deep mixing in detail based on the experience and research efforts accumulated in the past 50 years.