Laser-induced breakdown spectroscopy (LIBS), known for its rapid, multi-elemental, and stand-off analysis capabilities, has emerged as a promising tool for deep-sea exploration. In recent years, various underwater LIBS instruments have been successfully developed towards the submarine applications. Despite its advantages, the behavior of laser-induced plasma in liquids presents challenges for spectroscopic analysis, especially when compared to plasma formed in gaseous environments. Underwater plasma emissions are often dominated by strong continuous radiation, with relatively weak spectral signals. Understanding the characteristics of underwater plasma, particularly under high-pressure conditions, is essential for optimizing the use of LIBS in deep-sea applications. This chapter provides an overview of recent advancements in underwater LIBS, focusing on the spatio-temporal behaviors of laser-induced plasma in water, efforts to enhance signal sensitivity and stability, the impacts of high pressure on LIBS measurement, and the developments of instrumentation for deep-sea exploration.