A theoretical model is developed to describe the polarization and depinning of charge-density waves (CDW's) in the inorganic linear-chain compounds which exhibit Fr\"ohlich sliding conduction. Each individual impurity within the crystal is assumed to pin the CDW phase very strongly at the impurity site, and dc CDW motion is made possible only by phase slip. Simple estimates are obtained for most observed properties of sliding CDW systems with use of a three-dimensional Ginzburg-Landau analysis. These predictions are found to be in excellent quantitative agreement with available experimental data characterizing virtually every aspect of CDW dynamics.