Wetting near grain boundaries is a fairly new topic in comparison with wetting at substrates (or walls). A Landau theory is reviewed that describes the wetting and interfacial unbinding transitions near grain boundaries (or defect planes). The results are compared with those for wetting at substrates. Restricting attention to short-range substrate-adsorbate forces, critical-point wetting (as conjectured by Cahn) applies for substrates, but not for grain boundaries, unless the grain boundary remains ordered at the bulk critical point. It is argued that, quite generally, surface order at the bulk critical point implies critical-point wetting. In this article I review some key results of our studies of adsorption and wetting near grain boundaries [1, 2]. At the same time I present new arguments and conjectures, which clarify and update the framework of understanding that is emerging.