  In this paper, we study moral hazard problems in contract theory by adding an
exogenous Planner to manage the actions of Agents hired by a Principal. We
provide conditions ensuring that Pareto optima exist for the Agents using the
scalarization method associated with the multi-objective optimization problem
and we solve the problem of the Principal by finding optimal remunerations
given to the Agents. We illustrate our study with a linear-quadratic model by
comparing the results obtained when we add a Planner in the
Principal/multi-Agents problem with the results obtained in the classical
second-best case. More particularly in this example, we give necessary and
sufficient conditions ensuring that Pareto optima are Nash equilibria and we
prove that the Principal takes the benefit of the action of the Planner in some
cases
