The dominant explanation for forgetting in cognitive psychology is that similar memories form competing associations, leading to interference at retrieval. Yet, more recent theories suggest that processes of interference and decay interact, allowing for an efficient and adaptive memory system that is able to cope with constant environmental changes. The present thesis aimed to explore this relationship in visual memory for 200 scenes. The degree of interference was manipulated by altering the number of images in a semantic category, from one per category (low interference) to five per category (high interference). Memory was tested by two-alternative forced-choice both immediately following encoding, and after 168 hours (one week). As hypothesised, this manipulation uncovered a significant interaction, which was replicated across two experiments. Over the period of a week, scene images encoded under low interference decayed more rapidly than those encoded under high interference. This pattern is consistent with a memory system that organises decay processes based on the posterior likelihood that memories will have future behavioural relevance. This is the first known study to investigate the relationship between interference and forgetting over time in long term memory, and it indicates that the processes of forgetting are indeed more complex than the traditional characterisation of decay and interference as competing and dichotomous theories.