We have made a detailed study of the structural and kinematic properties of lenticular and earlyand late-type spiral galaxies with bars, aiming to explore the formation and evolution processes of stellar bars in galaxies and their implications on the global formation and evolution of galaxies. First, using high signal-to-noise spectra obtained along the major and minor axes of the bars in a sample of 14 face-on galaxies, we have determined the line-of-sight stellar velocity distribution in the bars’ vertical axis in several points reaching 20 from the center. This was done with an algorithm properly developed for this task, which parameterizes the velocity distribution using a Gauss-Hermite series (see, e.g., R. P. van der Marel & M. Franx 1993, ApJ, 407, 525), allowing for an accurate determination of the kinematical parameters. These spectra were observed with the 1.5 m ESO telescope at La Silla, Chile, and with the 2.3 m Steward Observatory telescope on Kitt Peak, Arizona. With these data, it was possible to develop a diagnostic tool that allows one to estimate the ages of bars and distinguish between recently formed bars and evolved bars. Furthermore, we could evaluate the vertical structure of disks and bars in galaxies. We were able to separate evolved bars from recently formed ones based on the assumption that bars form within disks, thus initially having a thin vertical structure, which can be recognized by low values for the vertical stellar velocity dispersion . As bars age, processes like vertical resjz onances (e.g., F. Combes & R. H. Sanders 1981, A&A, 96, 164) and the hose instability (e.g., D. Merritt & J. A. Sellwood 1994, ApJ, 425, 551) contribute to make higher, i.e., turning jz them vertically thick and possibly originating the characteristic boxy/peanut morphology (see Fig. 1). Second, through realistic N-body simulations with NEMO (P. J. Teuben 1995, ASP Conf. Ser., 77, 398) that represent a 2–3 Gyr evolution of isolated galaxies with bulge, disk, and a rigid dark matter halo, we have studied the conditions necessary to the formation of bars in galaxies with different morphological types (i.e., different bulge/disk ratios). In this way, we could also check the timescales involved in the processes that