4. Conclusions
There is by now a relatively large literature measuring the cross border effects of conventional and unconventional monetary policies. This special issue contains some additional contributions to this literature, and in addition focuses on the implications for monetary policy cooperation. One key conclusion is that the desirability of cooperation is highly model specific and some potentially important shocks and propagation channels are still poorly understood. Given the state of our knowledge, it is better to be cautious before drawing policy conclusions. More research is thus needed. The special issue also touches upon the political economy and practical dimension of cooperation that are typically glossed over in the academic literature but in practice are important factors in determining whether cooperation arises or not. The complexity of cooperation from a legal and institutional point of view and differences in the understanding of the economy and propagation channels are likely to prevent cooperation outside of crisis times. In this respect, investigating simple forms of cooperation, for example through simple cooperative rules (Benigno and Benigno, 2006), seems a useful avenue for future research.