This article reviews recent studies on memory systems in humans and nonhuman primates, highlighting three key findings: (1) the capacity for nondeclarative (nonconscious) learning can be assessed through various tasks such as classification learning, perceptuomotor skill learning, artificial grammar learning, and prototype abstraction; (2) the entorhinal, perirhinal, and parahippocampal cortices are essential components of the medial temporal lobe memory system that supports declarative (conscious) memory; and (3) bilateral damage limited to the hippocampal formation can produce severe anterograde amnesia and temporally graded retrograde amnesia covering up to 25 years in humans. The article discusses the distinction between declarative and nondeclarative memory, emphasizing that amnesic patients, who have bilateral damage to medial temporal lobe structures, perform poorly on conventional memory tests but excel in tasks assessing nondeclarative memory. Recent studies have expanded the list of intact learning and memory abilities in amnesic patients, providing insights into the organization of memory and brain systems. The article also explores the role of the medial temporal lobe in declarative memory, particularly in monkeys, and the findings from human cases confirming the importance of the hippocampal formation in memory function.This article reviews recent studies on memory systems in humans and nonhuman primates, highlighting three key findings: (1) the capacity for nondeclarative (nonconscious) learning can be assessed through various tasks such as classification learning, perceptuomotor skill learning, artificial grammar learning, and prototype abstraction; (2) the entorhinal, perirhinal, and parahippocampal cortices are essential components of the medial temporal lobe memory system that supports declarative (conscious) memory; and (3) bilateral damage limited to the hippocampal formation can produce severe anterograde amnesia and temporally graded retrograde amnesia covering up to 25 years in humans. The article discusses the distinction between declarative and nondeclarative memory, emphasizing that amnesic patients, who have bilateral damage to medial temporal lobe structures, perform poorly on conventional memory tests but excel in tasks assessing nondeclarative memory. Recent studies have expanded the list of intact learning and memory abilities in amnesic patients, providing insights into the organization of memory and brain systems. The article also explores the role of the medial temporal lobe in declarative memory, particularly in monkeys, and the findings from human cases confirming the importance of the hippocampal formation in memory function.