This chapter examines various methods and techniques for detecting, assessing, and monitoring damage in concrete and steel structures. It covers a wide range of damage types, including corrosion, fatigue, impact, fire, earthquake, burst, cracks, fractures, anomalous shape change, abnormal deflections, abnormal bending, abnormal vibration, and unbalance. The importance of identifying and addressing structural damage to ensure safety and integrity is emphasized. The non-destructive testing (NDT) methods such as visual inspection, ultrasonic inspection, magnetic particle inspection, radiographic testing, and eddy current inspection is discussed. It also explores imaging techniques, quasi-static loading, structural monitoring, and artificial intelligence (AI) techniques for damage detection. Additionally, structural health monitoring (SHM) methods, including Acoustic Emission Testing (AET), the PZT-Based Active Wave Method, noise emission control, vibration-based methods, strain-based methods, and the utilization of machine learning algorithms, were investigated. The advantages, limitations, and applications of each method are highlighted, emphasizing the need for a comprehensive approach that combines multiple techniques for effective structural health assessment. The conclusion included discussing data collection and analysis methods, such as sensor data, seismic observations, visual data, and satellite data, along with imaging techniques like thermography, magnetic imaging, radar imaging, and electrical imaging. By utilizing these methods and techniques, engineers can enhance their understanding of structural health and make informed decisions to ensure the safety and longevity of critical infrastructure.