This manual discusses the emerging Chemical, Biological, Radiological, Nuclear (CBRN) operational doctrine of the Philippine Army (PA). The content is largely based from US FM 3-100 (Chemical Operations Principles and Fundamentals), US FM 3-101 (Chemical Staffs and Units), and the US FM 3-11 (Chemical, Biological, Radiological, Nuclear Operations), published in 1993, 1996 and 2019, respectively. Other references include local manuals from the Philippine Army, all of which shape the context of CBRN defense. This also introduces concepts of CBRN in protection as warfighting function and the dimension of CBRN in the Landpower Maneuver Concept. It also provides readers with doctrinal guidance on CBRN units during combined arms and other ground operations. Hence, it explains the concepts of, and details the procedures under: 1) CBRN defense capability and interplay in the operational environment; 2) CBRN Support in Full Spectrum operations; and 3) in-combat sustainment of units, while they perform full-spectrum operations in a CBRN environment. It also provides guidance on the administration, training development, and illustrates the CBRN units in force development.