Semantic content knowledge and ability to process that knowledge are both necessary. Theories of semantic memory have tended to focus on knowledge content. Semantic memory impairments in patients with neurodegenerative diseases, manifested in difficulties naming, recognizing, or describing objects, are well documented. Neurologically healthy individuals, including the elderly, are able to appropriately use similarity-or rule-based categorization, both in daily functioning and in controlled studies. This chapter details some work investigating semantic knowledge and semantic categorization processes. The novel animal categorization task was designed to separate content from process and to relate the findings to semantic memory. Processing matters and it may be that category-specific deficits arise because different categories are more or less conducive to particular categorization processes, which can be selectively compromised. Additionally, knowledge of the diagnostic status of features, as well as executive resources, appears to be a necessary component of rule-based processing.