The aim of this thesis was to contribute to a deeper understanding of cognitive processes influencing prospective memory performance in old age. Prospective memory is defined as the realization of activities intended for future execution. Four studies using cognitive neuroscience methods were conducted. In the first study healthy old adults were compared to patients with impaired executive functions and normal episodic memory showing that their executive, but not their episodic memory deficits, diminish their prospective memory performance. The second study demonstrated that a memory advantage for actions intended for future enactment as compared to actions intended for future report is based on an additional activation of motor brain regions during encoding, indicating that preparatory motor processes enhance their later retrieval. The third study found a similar memory advantage for to-be-enacted actions and a similar brain activation during their encoding for young and old healthy adults, suggesting that these preparatory motor processes are unaffected by aging. In the last study self-reports on everyday prospective memory competence did not discriminate between healthy old adults, patients in the preclinical and mild clinical stage of Alzheimer’s disease showing that these seem to be influenced by other than cognitive variables.