This article reviews the theory of Geoecology as a modern science in the geological and geographical series. There are propositions that geography of underground spaces will arise in the future due to intensive human use of the geological space, including the construction of intercity and international underground transport connections, large-scale underground urbanization, construction of underground industrial facilities, establishment and maintenance of underground conservation areas and tourism-and-recreation spaces, etc. The boundaries of the geographical shell are defined, the existing concepts of Geoecology (states, changes, and techniques) are briefly described and grouped. Special focus is on the geochemical aspects of the theoretical foundations of geoecological research. The following main reasons for the selection of the geological-geographical approach to Geoecology were defined: expansion of the geographical shell boundaries beyond the Earth’s surface; the penetration of life into all external geospheres, the existence of a deep biosphere; the manifestation of geodynamic processes on the earth’s surface, including the release of gases and emanations in zones of active faults and fractures on the Earth’s crust; the basic role of rocks in landscape formation (underground landscapes, sink and source of subsurface and underground water, soiland relief formation); utilization of underground spaces by humans. The two most important ecological and geochemical aspects of the geological-geographical approach are named. The first one has to do with the qualitative and quantitative chemical (elemental) composition of geospheres and components of geosystems, and the second one with the geochemical processes that generate the diversity of geochemical relationships both within each individual geosystem, and between different geosystems.