  The Liouville action emerges as the effective action of 2-d gravity in the
process of path integral quantization of the bosonic string. It yields a
measure of the violation of classical symmetries of the theory at the quantum
level. Certain aspects of the residual SL(2,R) invariance of the gauge-fixed
Liouville theory are disscussed. ( Lectures presented at the Danube Workshop
'93,
  June 1993, Belgrade, Yugoslavia.)
