  I review existing methods for determining mass-loss rates of red giants and
red supergiants based on infrared data. The simplest method is based on models
for the absorption and emission by dust which forms in the dense outflows from
these cool stars. I discuss the parameters and assumptions upon which the
method relies, review relationships between the mass-loss rate and infrared
colours or far-infrared flux density, and propose a new formula for the
mass-loss rate as a function of the visual extinction. I also briefly discuss
the use of atomic and molecular transitions at infrared wavelengths.
