The new century has witnessed a strategic breakthrough in unconventional oil & gas. Hydrocarbon accumulated in micro-/nano-scale pore throat shale systems has become an important domain that could replace current oil & gas resources. Unconventional oil & gas plays an increasingly important role in our energy demand. Tight gas, CBM, heavy oil and asphaltic sand have served as a key domain of exploration & development, with tight oil becoming a ‘bright spot’ domain and shale gas becoming a ‘hotspot’ domain. China has made great breakthroughs in unconventional oil & gas resources, such as tight gas, shale gas, tight oil and CBM, and great progress in oil shale, gas hydrate, heavy oil and oil sand. China has an estimated (223–263)×108 t of unconventional oil resources and (890-1260)×1012 m3 of gas resources. China has made a breakthrough for progress in unconventional oil & gas study. New progress achieved in fine-grained sedimentary studies related to continental open lacustrine basin large-scale shallow-water delta sand bodies, lacustrine basin central sandy clastic flow sediments and marine-continental fine-grained sediments provide a theoretical basis for the formation and distribution of basin central reservoir bodies. Great breakthroughs have been made in unconventional reservoir geology in respect of research methodology & technology, multi-scale data merging and physical simulation of formation conditions. Overall characterization of unconventional reservoirs via multi-method and multi-scale becomes increasingly popular and facilitates the rapid development of unconventional oil & gas geological theory, method and technology. The formation of innovative, continuous hydrocarbon accumulation theory, the establishment of the framework of the unconventional oil & gas geological theory system, and the determination of the implications, geological feature, formation mechanism, distribution rule and core technology of unconventional oil & gas geological study lays a theoretical foundation for extensive unconventional oil & gas exploration and development. Theories and technologies of unconventional oil & gas exploration and development developed rapidly, including some key evaluation techniques such as ‘sweet spot zone’ integrated evaluation and a six-property evaluation technique that uses hydrocarbon source, lithology, physical property, brittleness, hydrocarbon potential and stress anisotropy, and some key development & engineering technologies including micro-seismic monitoring, horizontal drilling & completion and “factory-like” operation pattern, “man-made reservoir” development, which have facilitated the innovative development of unconventional oil & gas. These breakthroughs define a new understanding in four aspects: ①theoretical innovation; ② key technologies; ③ complete market mechanism and national policy support; and ④ well-developed ground infrastructure, which are significant for prolonging the life cycle of petroleum industry, accelerating the upgrade and development of theories and technologies and altering the global traditional energy structure.