This chapter addresses the pivotal role of inspection in maintaining the integrity of pipelines laid in the challenging marine environment. Defects such as corrosion, cracks, and dents in steel pipelines, along with delamination, fiber breakage, and matrix cracking in composite pipelines, significantly compromise the structural integrity and operational efficiency of submarine pipelines, posing serious safety and reliability threats. Besides, defects in pipelines can also pose risks to the marine environment and human safety without proper maintenance strategies. This chapter looks into the significance of inspection methods and the latest developments in inspection technologies necessary for identifying defects and ensuring the ongoing, safe functioning of submarine pipelines. Figure 1.1 depicts a scenario in which a pipeline operator inspects a gas pipeline.