The use of a conceptual time surfaces as part of a sequence boundary has transformed sequence-stratigraphy to have chronostratigraphis significance. This application also results in a number of misconceptions and problems associated with boundary recognition and unit definition in sequence-stratigraphy. Like an unconformity used as a time barrier, both the interpretation of sea-level changes as mechanisms for sequence development and the inconsistence in the conceptual system of sequence-stratigraphy are important scientific problems in sequence-stratigraphy. Tracing the history of these problems is very useful to understanding the development of sequence-stratigraphy in the past 30 years and to further advancing sequence-stratigraphy as a discipline in stratigraphy.