Real-time estimation of what we will do next is a crucial prerequisite of purposive behavior. During the planning of goal-oriented actions, for instance, the temporal and causal organization of upcoming subsequent moves needs to be predicted based on our knowledge of events. A forward computation of sequential structure is also essential for planning contiguous discourse segments and syntactic patterns in language. The neural encoding of sequential event knowledge and its domain dependency is a central issue in cognitive neuroscience. Converging evidence shows the involvement of a dedicated neural substrate, including the prefrontal cortex and Broca's area, in the representation and the processing of sequential event structure. After reviewing major representational models of sequential mechanisms in action and language, we discuss relevant neuropsychological and neuroimaging findings on the temporal organization of sequencing and sequence processing in both domains, suggesting that sequential event knowledge may be modularly organized through prefrontal and frontal subregions.