I review the status of the issue of the k-string tension in Yang--Mills theory. After a summary of known facts I discuss a weakly coupled four-dimensional Yang--Mills theory that supports non-Abelian strings and can, in certain aspects, serve as a toy model for QCD strings. In the second part of the talk I present original results obtained in a two-dimensional toy model which provides some evidence for the sine formula.

PACS numbers: 12.20.--m, 11.27.+d, 11.15.Pg, 11.30.Pb