A new approach to bottom-up parsing that extends Augmented Context-Free Grammar to a Process Grammar is formally presented. A Processor Grammar (PG) defines a set of rules suited for bottom-up parsing and conceived as processes that are applied by a PG Processor. The matching phase is a crucial step for process application, and a parsing structure for efficient matching is also presented. The PG Processor is composed of a process scheduler that allows immediate constituent analysis of structures, and behaves in a non-deterministic fashion. On the other side, the PG offers means for implementing specific parsing strategies improving the lack of determinism innate in the processor.