Working papers are working documents disseminated by their authors, in order to solicit a preliminary informal discussion, before being sent to a scientific journal or before submitting a communication to a congress.
They are often made public on the website of an author or institution which he belongs to. In addition, several institutions publish working paper series made then available on their website for free. Among these you can find the "Department of Economics and Statistics Working Paper Series" of the Department of Economic, Social and Mathematical-Statistics sciences.
At the WP location, in the periodicals room, you can find paper versions of some working papers.