  Optical interferometry is the only technique giving access to milli-arcsecond
(mas) resolution at infrared wavelengths. For Cepheids, this is a powerful and
unique tool to detect the orbiting companions and the circumstellar envelopes
(CSE). CSEs are interesting because they might be used to trace the Cepheid
evolution history, and more particularly they could impact the distance scale.
Cepheids belonging to binary systems offer an unique opportunity to make
progress in resolving the Cepheid mass discrepancy. The combination of
spectroscopic and interferometric measurements will allow us to derive the
orbital elements, distances, and dynamical masses. Here we focus on recent
results using 2- to 6-telescopes beam combiners for the Cepheids X Sgr, T Mon
and V1334 Cyg.
