Global mountainous areas account for about 24 percent of the total global terrestrial area. The mountain area in China makes up approximately 65 percent of the national land area. Thus, China can be described as a mountainous country. Mountains are an important resource foundation and are a vital ecological defense for the existence and development of human beings. However, because of the special energy gradients, mountainous regions are centralized areas for the development of natural hazards. Besides, mountainous areas also serve as a sensitive indicator for global change studies because of their vertical environment gradient. Mountainous areas has become a hotspot and area of focus for many earth system studies. Remote sensing is one of the most important and effective tools for mountain studies. It can provide continuous spatio-temporal land cover, feature status, and historical change information. However, given the dramatically different geometric characteristics of mountainous surface and the various special ecosystem structures and functions, remote sensing applications in mountainous areas still face many challenges and difficulties, including serious geometric and radiometric distortion problems, more complex energy balance process, and more prominent ill-condition retrieving problem for ecosystem parameters than that of the plain area. Mountain remote sensing, which mainly focuses on the basic theories, methodologies, and integrated applications of remote sensing in mountainous environments, is a research branch of the remote sensing science. Although the word "mountain remote sensing" firstly began to be used in the middle 1980s, the research on remote sensing in mountainous areas can be tracked back to nearly 100 years ago because topographic mapping began early in the photogrammetry remote sensing field. In recent decades, issues regarding the basic theories and integrative applications of mountain remote sensing have attracted worldwide attention. Mountain remote sensing has become one of the most popular research areas in remote sensing sciences. We summarized the scientific significance and several frontier issues in mountain remote sensing studies. Currently, the main contents of mountain remote sensing research should include but not be limited to the following aspects:(1) the interaction mechanism and modeling theory between electromagnetic signatures and mountain land surfaces;(2) spatial-temporal-spectral normalization methodologies for mountainous remote sensing data;(3) remote sensing modeling, retrieving, and assimilation methodologies for land surface information in mountainous areas;(4) scaling effects and the validation of remote sensing products in mountainous areas; and (5) the integrated applications of remote sensing information in mountain studies. Currently, mountain remote sensing faces unprecedented developing opportunities because of the following reasons:(1) emerging novel remote sensing observation technologies, (2) in-depth development of basic theories and methodologies of mountain remote sensing, (3) driving forces from earth science big data studies, and (4) great application demands of mountain remote sensing. In this work, we reviewed the research progresses of basic theories and applications of mountain remote sensing in recent years, and analyzed the opportunities, challenges, and future prospects of mountain remote sensing in the modern era.