The private sector is one of the sources of finance included in developed countries' pledge in the UN climate negotiations to mobilise $100 billion annually by 2020 to support developing countries' efforts to address climate change. For adaptation in particular, it remains unclear what mobilised private finance is. Research so far has focused on its potential and experiences in developing countries, but not on the arguments of those who introduced and continue to advocate private adaptation finance: developed countries. This paper investigates the positions of developed countries and development banks and agencies. In particular, it aims to identify whether those actors can reach a common understanding of private adaptation finance that minimises norm conflicts in a fragmented climate finance system. Empirically, the paper examines the Biennial Reports and submissions on Strategies and Approaches for Mobilising Scaled-up Finance of six developed country parties, as well as data from interviews with experts from development banks and agencies. The analysis finds a number of discrepancies between these sets of actors, for example on motivations for and modes of private sector involvement. This discrepancy is the result of ambiguity around the concept of private adaptation finance in a highly fragmented climate finance architecture. This ambiguity is problematic when the aim of mobilising private adaptation finance is to contribute to the $100 billion commitment. However, if the aim is adaptation in practice, both ambiguity and fragmentation might actually make the climate finance system more inclusive and innovative.