Disc cutters are the key cutting tools of hard rock Tunnel Boring Machines (TBMs) and play a fundamental role in transmitting force to the rock and enabling continuous excavation. They are designed to withstand high stress and abrasion during tunneling. Their performance directly influences penetration rate, machine advance, and overall project efficiency. The wear and life of TBM disc cutters are affected by multiple parameters, including cutter metallurgy, rock strength and abrasivity, rock fracture patterns, in-situ stress conditions, and machine operational parameters such as thrust, rotation speed, and cutterhead design. Variations in these geological and mechanical factors can significantly accelerate the normal wear, reduce TBM penetration and cutter efficiency, and increase the frequency of cutter changes. Moreover, if wear exceeds the wear limit, cutters must be replaced to avoid damage to the TBM. Therefore, accurate prediction of disc cutter life is essential for reliable project scheduling, cost estimation, maintenance planning, and avoiding unexpected delays or financial overruns. In this regard, various empirical and theoretical life prediction models have been developed to estimate disc cutter wear in rock tunneling projects, supporting better planning and optimization of TBM performance. This chapter will address disc cutter wear in detail, from the basic mechanisms to prediction methods. The most applicable models will be introduced, and their formulations will be presented clearly. By the end of the chapter, the reader will be able to practically apply these models in a given project and use them to predict the life of disc cutters as initial input for planning and operational purposes.