This article analyses participant experiences and statements about perceived problems in two online conferences to identify tensions and disturbances relating to external factors, conference technology, online discussions and design choices and then considers the underlying contradictions within the conference systems which generate both positive and negative experiences of participation. The analytic stance is based on cultural historical activity theory (CHAT) since this approach gives a framework to understand and explain dilemmas, tensions, disturbances and possible contradictions as drivers for change in socio-technical systems. The article ends with reflections on the implications for designers of online conferences as convenors and technology stewards.