Abstract: As a type of geological hazard induced by multiple interacting factors, landslides exhibit frequent occurrence, high complexity, and considerable uncertainty, thereby necessitating the development of an efficient and integrated monitoring system. This paper provides a systematic overview of advances in landslide monitoring technologies under the “space–air–ground–sea” framework. Currently, monitoring of subaerial landslides is relatively well developed, covering ground-based geodetic measurements, three-dimensional laser scanning, subsurface displacement monitoring, and multiphysics monitoring; in parallel, spaceborne InSAR, GNSS, and optical remote sensing facilitate the capture of macroscopic deformation signals; airborne platforms, using UAVs and LiDAR, further improve high-precision detection and compensate for observational blind spots in critical areas. It is important to note that submarine landslide monitoring is still in the exploratory phase; in shallow-water settings, it primarily depends on multibeam surveys, side-scan sonar, and shallow profiling, whereas monitoring of deep-sea seafloor landslides mainly relies on field investigation, in situ observation, physical modeling, and numerical modeling. Given the marked differences among various landslide types in their hazard-prone environments, key monitoring objects, and technical constraints, this study conceptualizes “space–air–ground–sea” as a platform coordination framework oriented toward different application scenarios. The purpose of this framework is to selectively mobilize and combine spaceborne, airborne, ground-based, and sea-based technologies according to landslide type and monitoring objectives across different scenarios, so as to support risk detection, process analysis, and early warning decisions.