Bars are believed to be major drivers of secular evolution of lenticular and spiral galaxies through interactions with the outer disk and dark matter halo. Understanding bars is therefore vital for understanding how disk galaxies evolved and acquired their present properties. This lecture series will introduce students to barred galaxies, their observational properties, stellar and gas dynamics, formation process and evolutionary path. The interplay between bars, supermassive black holes, bulges, disks, and dark matter halos will be investigated by comparing theoretical predictions to observational data and numerical simulations.