Abstract : This thesis rests on the statement of fact: precautionary saving which stems from the incompleteness of insurance markets and the existence of borrowing constraints (Aiyagari ) turns out to be important (Skinner , Caballero  Kasarosian ). This mechanism is likely to modify the impact of redistribution and insurance policies. The precautionary saving behaviour depends on the level of idiosyncratic income risk. The goal of redistribution and insurance programs is to reduce the idiosyncratic income risk. Therefore, they are likely to interact with the precautionary saving behaviour. The thesis project is to get the precautionary saving mechanism into the assessment of the insurance and redistribution policies. Four tools of economic policy are investigated: the income and inheritance tax, the unemployment insurance and public debt.
The current progressivities of income and inheritance tax reduced wealth inequality in the same proportion, however, modify differently the saving behaviour. The progressivity of the income tax reduces the saving of the richest households whereas the progressivity of the inheritance tax leads the poorest households to save for bequest motive.
Contrary to Cahuc et Lehmann , we show that a declining profile of unemployment benefits is able to reduce the trade-off between efficiency and equity when we take account of precautionary saving mechanism. The short term unemployed begins to save whereas he does not do when unemployment benefits are constant over time. Then, he can dissave to support his consumption when the unemployment episode goes on.
Ayagari and McGrattan  show that taking precautionary saving into account reasserts the positive role of public debt. However, they take no account of aggregate risk which increases idiosyncratic income risk. Therefore, they have under estimated the role of public debt. During recession the unemployment rate and the unemployment duration increase.
Precautionary saving is less likely to be able to smooth consumption. Moreover during recession the interest rate is smaller. It is more difficult to save for precautionary motive because the cost of this self insurance is higher. The introduction of public debt in such environment enables to increase the interest rate. Precautionary saving becomes less costly. That is why aggregate risk leads to revise upwards the optimal level of public debt.