Against a background of the low engagement of small to medium-sized enterprises (SMEs) in e-business this thesis investigates the emergence of, and potential for, critical e-aggregation applications defined as 'an e-business application, promoted by a trusted third party, which engages a significant number of SMEs by addressing an important shared business concern within an aggregation'. By using a triangulation of methodologies, namely qualitative case study, participant observation, context monitoring and quantitative survey the research shows that such applications can facilitate the e-business engagement of SMEs. Context monitoring is a proposed method of continuous appreciation, which was necessary because of the constantly changing environmental conditions during the period of the study. There were six key findings, namely (i) higher levels of e-business engagement by SMEs in aggregations, (ii) the emergence of critical e-aggregation applications, (iii) the emergence of collaborative 'one to many' business models, (iv) the importance of trusted third parties, (v) the deliberate accumulation of strategic information, and (vi) evidence of increased structure and integration. Significantly this work takes deliberately dual, user and provider, perspectives. The supporting literature review drew from both praxis and three areas of theory, namely IT adoption by SMEs, inter-organisational networks (IONs) and e-business models, in order to construct an interpretative framework for the dimensions of aggregations. In terms of future research the importance of a better conceptual understanding of complexity on the adoption of IT by SMEs and the impact of critical e-aggregation applications on business markets were highlighted.