ABSTRACT: Chronostratigraphy has a “prehistory†beginning with Leonardo’s and Steno’s twofold relative geologic time division. It developed further with Marsili’s (1728), Lehmann’s (1756), Arduino’s (1759-60) and Werner’s (1787) threefold, fourfold, and fivefold divisions respectively. Meanwhile, the initial steps were being taken in understanding Earth’s chronometry. Geological mapping exponentially increased the number of lithostratigraphic and chronostratigraphic units and forced the need for a common language and practice by international agreement. That objective became feasible with the establishment of the International Geological Congress (IGC), and the bipolar or dual classification of chronostratigraphic and chronologic units was formally established during the 2nd IGC in Bologna in 1881. Chronostratigraphic classification has displayed a remarkable nomenclatural stability, notwithstanding continuously changing criteria of use, correlation, improvement, and redefinition of the standard chronostratigraphic units. The development of chronostratigraphy was by scientific research and the necessary stability was through the IGC, as it appears from this review of the main chronostratigraphic resolutions and recommendations adopted by the IGC sessions from Bologna in 1881 to Sydney in 1976. An hierarchical classification and an historical approach underpin the evolution of chronostratigraphic classification. Five stages of evolution are outlined. Their succession illustrates changing paradigms, ongoing improvement by new tools of correlation, and the stability of names defined and used in a permanent common language. This flexibility should guide future developments in chronostratigraphy.