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The serotonin 1A (5-HT(1A))-receptor is involved in a wide range of physiological functions, but has also been implicated in the pathophysiology of anxiety disorders and depression. Although the 5-HT(1A)-receptor is one of the best described receptor subtypes of the serotonergic system, its complex distribution pattern, pre- and postsynaptic localisation, and its impact on various neurotransmitters aggravate the attribution of 5-HT(1A)-agonistic effects to behavioural outcomes. The role of 5-HT(1A)-receptors for cognitive processes seems undisputed. However, the exact involvement of pre- and postsynaptic sites remains unexplained. Genetically modified animals are a complementary approach to pharmacological studies for further investigations of the role of the 5-HT(1A)-receptor. Next to 5-HT(1A)-receptor knockout mice, two transgenic mouse lines exist that either overexpress the 5-HT(1A)-receptor transiently or permanently. The latter mouse line stands out due to the fact that a distinct overexpression is primarily found in the outer cortical layers and hippocampus, both projection areas of serotonergic neurons. Here, we discuss the findings obtained from 5-HT(1A)-receptor knockout and overexpressing mice concerning their learning and memory abilities.