In this chapter, we review the specialized literature and identify the key factors influencing employment structures over the past few decades. We examine the impacts of globalization and international trade, deindustrialization, tertiarization, deagrarianization, technological change, population ageing, migration, shifts in gender relations and female labour market participation, economic and employment policies, consumption spillovers and cyclical economic developments. For each factor, we explore how it may affect employment and discuss the surrounding debates regarding its potential impacts. Also, we review the evidence and theories of occupational change, analysing the main findings (such as prevailing patterns of change in different places) and the drivers and hypotheses proposed as explanations. The aim of this chapter is to establish a theoretical and conceptual framework for the subsequent analytical chapters, providing a toolkit to interpret subsequent findings.