The literature on shock-responsive social protection focuses  on operational features that improve the speed and reach of  the response, but little is known about the optimal design  of emergency social protection responses in terms of which  programs to use, information about the people affected, and  the extent of their losses. This paper studies optimal social  protection responses to shocks, using microsimulations of  different social assistance responses in Albania, Moldova,  and North Macedonia. The paper shows that optimal  design depends not only on the magnitude of the shock, but  also on how the shock affects welfare rankings and on the  parameters of the existing social assistance system, including the generosity of the schemes and how well they cover  the poor.