A business ecosystem is a community of multiple co-evolving actors with interdependent product offerings organized around a specific value proposition. While the extant literature focuses on these two structural elements of ecosystems that existed ex ante, we challenge this notion with our core discovery that ecosystem actors emerge in an ex post dynamic process. With a longitudinal qualitative study of the vertically disintegrated part of the Chinese mobile phone industry, we develop a two-dimensional process model of ecosystem emergence, namely the temporal dimension that delineates three processal stages of ecosystem emergence and the spatial dimension that highlights an architectural pattern of reciprocities between value chain and resource pool to enable the ecosystem emergence. We also offer inter-temporal enabling conditions during ecosystem evolution. These findings enable us to complement the ecosystem literature by elaborating the antecedents, outcomes, and enabling conditions of ecosystem emergence in relation to multiple types of ecosystem actors. We also shed light on the value chain (re-)configuring process which derives from the reciprocity between value chains and ecosystem resources.