  Since 2008 we have run an observational program to accurately measure the
characteristics of known exoplanet systems hosting close-in transiting giant
planets, i.e. hot Jupiters. Our study is based on high-quality photometric
follow-up observations of transit events with an array of medium-class
telescopes, which are located in both the northern and the southern
hemispheres. A high photometric precision is achieved through the
telescope-defocussing technique. The data are then reduced and analysed in a
homogeneous way for estimating the orbital and physical parameters of both the
planets and their parent stars. We also make use of multi-band imaging cameras
for probing planetary atmospheres via the transmission-photometry technique. In
some cases we adopt a two-site observational strategy for collecting
simultaneous light curves of individual transits, which is the only completely
reliable method for truly distinguishing a real astrophysical signal from
systematic noise. In this contribution we review the main results of our
program.
