The classification of line tension has been given distinguishing between the mechanical line tension and the thermodynamic one as related to the excess mechanical stress at the phase linear boundary and the specific work of formation of a new linear phase boundary, respectively. Three types of line tension are characterised: the line tension in two-dimensional heterogeneous systems, the line tension at the three phase contact line, and the effective line tension in the presence of deformation along the three phase contact line. Phase transitions in two-dimensional systems, the effect of roughness of the three phase contact line and the anisotropy of the contact angle on deformed elastomeric surfaces have been discussed. Copyright (C) 1999 Elsevier Science B.V.