Moisture is the key factor affecting the physical and mechanical properties of wood as well as its storage, processing and use. Therefore, the relationship between wood and moisture has always been one key research topic in wood science. Early studies focused on the measurement of moisture content of wood and the establishment and modification of the model of moisture content. With the application of high speed computer and advanced analytical instrument with spatial resolution, new studies on moisture distribution and existing state in wood are emerging. Here, this book is about the above key issues in the study of the relationship between wood and moisture, the distribution and existing states of moisture in wood. In this book, it was focused on the distribution and existing states of moisture in the wood cell wall by using micro-FTIR spectroscopy and confocal Raman spectroscopy. Based on these, the theoretical sys of the moisture sorption of wood at the cellular and molecular level can be established and the theoretical guidance to improve these technologies of wood modification, wood drying and preparing the high-value wooden material can be provided.