Through thermodynamic analyses of several liquid crystals (LCs) and related compounds, discussed are the roles played by alkyl chains attached to mesogenic cores. The roles identified include, i) an extension of molecular length, enhancing the shape anisotropy required for the formation of LCs by excluded volume effects, ii) an entropy reservoir, which, through the entropy term in Gibbs energy, stabilizes mesophases and governs the phase relation, and iii) intramolecular solvent (self-solvent), which induces micro-phase separated LCs including SmA phase. The last aspect opens the possibility that science and technology of thermotropic and lyotropic LCs be combined under the unified view of LCs. The implication of such a view on structures of layered LCs such as SmA phase is briefly discussed.