Ices on satellites in the solar system undergo changes produced by meteoritic bombardment, pressure, and thermal effects. The effect of the meteoritic bombardment on (porous) ices is some densification, but mainly the formation of crystalline H 2O polymorphs and the establishment of a rough equilibrium ratio between hexagonal and amorphous forms below 150°K. As a result of the low temperatures, the pressure densification of porous ices is significant only at depths of at least hundreds of meters for large satellites. The densification process is controlled by creep, that is, by slow plastic deformation of the solid matrix for medium porosities and by diffusion for low porosities. The isothermal effect on porous ice is an extremely slow densification process caused by surface and volume diffusion. A thermal gradient leads to migration of pores toward the warmer end and, since the velocity of the pores is proportional to their size, to their clustering. As a result, smaller pores become eliminated and the pore size distribution changes. Quantitative analysis of these effects has been made for ices including the integrodifferential coagulation equation which gives the new pore size distribution and the steepening of the gradient of porosity. For CO 2-ice the rates of these effects can be estimated to be several orders of magnitude higher than for H 2O-ice. Various physical properties are significantly affected and, in particular, it is concluded that, on a time scale of 10 8 to 10 9 years, in satellites with a cold interior the outer icy layers may have become densified while the opposite is true when satellites such as Europa and perhaps Enceladus have an internal source of heat.