Intrusive memories are a core symptom present in various psychological disorders. This thesis investigates the neural networks underlying intrusive memory processes using functional magnetic resonance imaging (fMRI). Study 1 utilised an emotional face paradigm to examine the relationship between emotional processing and reexpe- riencing in posttraumatic stress disorder (PTSD). Results suggest that in individuals who experience reexperiencing symptoms, viewing emotional faces is associated with neural networks implicated in cognitive and emotional control, emotional awareness, attentional processes and enhanced visual processing. Flashbacks in particular were associated with greater generalised activations in brain regions associated with emotional and sensory processing. Study 2 investigated encoding of intrusions in healthy participants, who viewed negative and neutral images during fMRI. Results suggest that in order for a memory to become intrusive, brain networks involved in emotion-related processes such as fear processing, emotional and cognitive control, and interoception are active at encoding. Study 3 investigated the role of mode of processing in encoding of intrusions in healthy participants, comparing neural activity during encoding under visual and verbal processing conditions. Results suggest that encoding of intrusions is related to activity in brain regions that are involved in emotion processing, and emotional and behavioural suppression. Contrary to predictions based on major models of intrusions, emotion-related activations were only seen under verbal processing conditions. This finding does not support theories proposing that perceptually driven processing at encoding is more likely to result in intrusions. Finally, in Study 4 a novel version of the trauma film paradigm was used to investigate retrieval of intrusions in healthy participants. During intrusion retrieval, unique activations occurred in the middle temporal gyrus and cerebellum, suggesting that intrusion retrieval may be distinguished by emotion-related processing. Taken together, these findings provide evidence for the importance of emotional processes in intrusive memories. This program of research provides preliminary neuroimaging evidence of the neural networks involved in intrusive memory processes, and extends current models of intrusive memories.