Intervening in the FX market implies a complex decision process for central banks. Monetary authorities have to decide whether to intervene or not, and if so, when and how. Since the successive steps of this procedure are likely to be highly interdependent, we adopt a nested logit approach to capture their relationships and to characterize the prominent features of the various steps of the intervention decision. Our findings shed some light on the determinants of central bank interventions, on the so-called secrecy puzzle and on the identification of the variables influencing the detection of foreign exchange transactions by market traders. Financial support from the Belgian National Fund for Scientific Research (FRFC Program) is gratefully acknowledged. We would like to thank Cinzia Cirillo for computational assistance as well as Agnès Bénassy-Quéré for providing us with estimates of the fundamental exchange rate value. We are also grateful to Gabriele Galati for sharing his dataset that allows to make some cross-checks with our findings. We thank participants of seminars and conference held in Luxembourg, Paris Nanterres and at the Bank of Canada for comments and suggestions, and in particular G. Galati, C. De Souza and R. Miller. The usual disclaimer applies.