This open access book serves as a comprehensive exploration of Alternating Current Field Measurement (ACFM), encompassing the foundational theory crucial for subsequent chapters, as well as the design and testing of ACFM probes, instruments, and software. Providing guidance and serving as a reference for ACFM instrument development, the text delves into visualization research in ACFM, offering valuable insights for technical engineering applications. Nondestructive testing (NDT) emerges as a pivotal method for detecting and assessing defects, offering support for safety pre-warning and maintenance decisions in industrial structures. Originating from the 1980s, the demand for an NDT technique arose to inspect fatigue cracks at welded intersections in offshore underwater structures in the North Sea. Conventional NDT methods proved impractical in this distinct underwater environment with quantitative evaluation requirements, prompting the development of the ACFM technique by researchers in the mechanical engineering department at University College London. Over the past four decades, ACFM's theory model, inspection methods, and equipment have undergone rapid advancements, gaining widespread utilization in ocean engineering, the power industry, rail traffic, and special equipment fields. This book encompasses diverse facets, including the global development history of alternating current field measurement technology, core basic theory, signal processing methods, probe instrument development, standardization construction, and engineering applications. Serving as a valuable learning reference for students and offering fundamental theoretical guidance for scientific researchers, it also provides case introductions for engineering applications. The book aims to propel both theoretical research and practical applications of alternating current field measurement technology, contributing significantly to its popularization and widespread application.