Download the PDF. Great paper!

In considering fiscal policy at this juncture, policymakers need to answer several key questions. Is fiscal stimulus needed? When should such stimulus be provided? And what would constitute effective fiscal stimulus? These questions are not merely technical. The livelihoods and living standards of many Americans are at stake. Fortunately, economic research provides clear theory and evidence for making appropriate decisions about if, when, and how to craft fiscal stimulus. This paper summarizes the evidence and provides straightforward principles and examples for formulating effective stimulus.

If, When, How: A Primer on Fiscal Stimulus - Brookings Institution