This chapter begins to modify our view of single hypothetical structure (STM) and to replace it with the concept of working memory (WM). It moves away from a strategy of exploring the capacities and implications of a STM and towards a more functional analysis. WM refers to the role of temporary storage in information processing. The concept of WM with its implication of a limited capacity system for holding and manipulating information has motivated research in a number of areas. The model subdivided WM into three components; Central Executive, Articulatory Loop and Visuo-Spatial Scratch Pad (VSSP). Attempts to analyse the articulatory loop in more detail have thrown up a number of apparent anomalies. The concept of a VSSP provides an appropriate framework for integrating work on visual imagery such as that popularized by Shepard and his coworkers with work on individual differences in imagery and spatial intelligence tests.