Within the context of housing associations as fluid third sector hybrid organisations, this paper examines the dynamics of strategic decision-making in relation to diversification into the market rented sector. A convergence of factors shaped an agenda for associations to engage with such commercial activity, crystallising debates about opportunities versus tensions and the remit of organisations. Qualitative research with senior housing association professionals operating in Northern England illustrates the significance of external local and internal organisational contexts in making and justifying decisions; this is highlighted within an emergent typology of organisational responses. Depending upon interpretation, the interplay between social and financial justifications varied, including legitimising activity within a broader social purpose. The potential for (re)interpreting parameters illustrates the importance of understanding the variety and complexity of interacting dynamics that influence the strategic decisions of third sector hybrid organisations and what they deliver at the local level.