This book systematically introduces readers to the finite element analysis software DIANA (DIsplacement ANAlyzer) and its applications in civil engineering. Developed by TNO Corporation in the 1970s, DIANA is frequently used in civil engineering and engineering mechanics. Unlike the software user's manual, which provides a comprehensive introduction and theoretical analysis, this book presents a simplified overview of the basic background theory to help beginners master the software quickly. It also discusses GUI operation and the command console in Python language, and includes examples involving classical modeling operations to help readers review each section. Both the book and DIANA itself are valuable resources for students and researchers in all the structural engineering fields, such as civil engineering, bridge engineering, geotechnical engineering, tunnel engineering, underground structural engineering, irrigation, municipal engineering and fire engineering.