Yvelines' 10th constituency covers the largely rural southern territory of the department and is its largest seat.

However, in 2010 the seat was won in a by-election Anny Poursinoff of the EELV.

The seat returned to its historic pattern in 2012 when it elected the man she defeated in that by-election Jean-Frédéric Poisson of the PCD.

[4] MP Christine Boutin's resignation in 2009 precipitated a by-election, which was won by UMP candidate Jean-Frédéric Poisson with a lead of just five votes over Greens candidate Anny Poursinoff.

[5] An appeal and recount led the Constitutional Council to first declare Poisson had won by just one vote, and then ultimately to order a fresh by-election which was held on the 4th and 10 July 2010.