This thesis, a qualitative study, examined the literacy practices of nine workers who self-report literacy difficulties. Through a series of interviews it specifically investigated how, in the course of their daily work, their mediated behaviour resulted in development of literacy competence. Through analysis of the workers’ experiences this thesis explored sociocultural themes deriving from Vygotskian traditions such as the central mediational role of psychological tools and signs and the importance of activity taking place in social settings. It took the theoretical position that literacy is an increasingly complex construct that extends beyond functional connotations such as reading, writing and spelling. It focused on the kinds of literacy skills that individuals require in a world characterised by rapid and frequent changes. In doing so this thesis recognised the diverse modalities in literacy performance that emphasise ways of knowing and ways of doing or designing as well as reading, writing, listening, thinking, speaking and comprehending across a range of modalities. This thesis argues that sociocultural concepts are applicable to adult learners. In particular it concludes that adult learners in the course of their jobs demonstrate a repertoire of literacy competence through engagement in meaningful literacy practices. This thesis reports that a significant indicator of the reported broadening in literacy competence is the support structures available in the workplace and in particular the specific characteristics of mentors / Doctor of Philosophy (PhD)