Title: "Interferometric views on Cepheids: from a simple problem to a 
new perspective."

Abstract: Cepheids have been known for a century to be distance 
indicators, and the quest to calibrate their Period-Luminosity (PL) 
relation is still on. 10 years ago, the diameter variations of a Cepheid 
was directly detected by interferometry and paved the way towards the 
best calibration of the PL relations, using the parallax pulsation 
method. While pushing the method to the limits (with a precision on the 
distance approaching the 1%), it became clear that the hypothesis on 
which the method was relying had to be rethought. I will present the 
progression of interferometric results that led to different results: 
the realization that Cepheids' photospheres cannot be treated as 
hydrostatic; the (re)-discovery of circumstellar envelopes and so on.