This study addresses the dynamics of the issue space in multiparty systems by examining to what extent, and under what conditions, parties respond to the issue ownership of other parties on the green issue. To understand why some issues become part and parcel of the political agenda in multiparty systems, it is crucial not only to examine the strategies of issue entrepreneurs, but also the responses of other parties. It is argued that the extent to which other parties respond to, rather than ignore, the issue mobilisation of green parties depends on two factors: how much of an electoral threat the green party poses to a specific party; and the extent to which the political and economic context makes the green issue a potential vote winner. To analyse the evolution of the green issue, a time-series cross-section analysis is conducted using data from the Comparative Manifestos Project for 19 West European countries from 1980–2010. The findings have important implications for understanding issue evolution in multiparty systems and how and why the dynamics of party competition on the green issue vary across time and space.