  Prompted by work on the buckling instability in barred spiral galaxies, much
effort has been devoted lately to the study of boxy/peanut-shaped (B/PS)
bulges. Here, we present new bar diagnostics for edge-on spiral galaxies based
on periodic orbits calculations and hydrodynamical simulations. Both approaches
provide reliable ways to identify bars and their orientations in edge-on
systems. We also present the results of an observational search for bars in a
large sample of edge-on spirals with and without B/PS bulges. We show that most
B/PS bulges are due to the presence of a thick bar viewed edge-on while only a
few may be due to accretion. This strongly supports the bar-buckling mechanism
for the formation of B/PS bulges.
