It is now generally accepted that Blue Straggler Stars (BSS) are more massive than the normal MS stars, and are the result of mass transfer between binary companions (MT-BSS), possibly up to the coalescence of the binary system, or merger of two single or binary stars driven by stellar collisions (COL-BSS).
To finally unveil their nature and their formation mechanisms, we are using several different and complementary approaches, including high-resolution and multi-wavelength photometric observations, deep high-resolution spectroscopy, and Monte-Carlo dynamical simulations.
This line of research has received a
remarkable boost in the last year thanks to the availability of the wide-field
camera LBC on the part-Italian 
m LBT telescope. This instrument is
ideal to obtain the very efficient multi-wavelength radial coverage of GCs
required for the detailed analyses of the BSS populations which we are performing.
In particular we have recently completed a thorough study of M53 (Beccari et al. 2008),
of NGC2419 (Dalessandro et al. 2008), NGC5466
(Beccari et al. 2009) and M2 (Dalessandro et al. 2009)
This work is in collaboration with F. Ferraro, E. Dalessandro, B. Lanzoni, A. Sollima (Univ. Bologna), G. Beccari (ESTEC, NL), R. Rood, R. Schiavon (Univ. of Virginia, USA), M. Mapelli (Zurich Univ., Switzerland), S. Sigurdsson (Pennsylvania State Univ., USA), E. Sanna (Univ. Roma Tor Vergata), A. Sills (McMaster Univ., Canada), C. Mancini (Univ. Firenze).