Working memory (WM) allows a limited amount of information to be temporarily stored in a state of heightened accessibility for use in ongoing processing. This thesis examined how increasing the relative value of one item affects performance on WM tasks. Chapter 2 explored whether this type of prioritisation differs from probe frequency, whereby one item is more likely to be tested than the rest. This pair of studies demonstrated that probe value and probe frequency are likely to involve distinct cognitive mechanisms. Chapter 3 then examined whether value effects can be observed in an auditory-verbal WM task, as research to date has investigated effects in the visual domain. Significant value effects were observed, which were not reduced in size when rehearsal and attentional resource mechanisms were reduced. Participants did, however, appear to abandon the less valuable items when both rehearsal and executive control resources were disrupted. Next, Chapter 4 investigated whether children can direct their attention to more valuable information in WM when sufficiently motivated to do so. Probe value effects were observed, although these were smaller than those previously reported in adults. There was also evidence that children selectively prioritised the more valuable item when it was likely to considerably enhance performance. Finally, Chapter 5 examined whether prioritising a more valuable item at WM can enhance performance on a surprise LTM task. A value effect was observed at LTM, but only when the more valuable item had been tested at WM. Taken together, these findings demonstrate that value effects in WM are distinct from other attentional manipulations and robust across modalities and groups. Prioritising a more valuable item for a WM test can also enhance longer-term retention if the item is assessed at WM.