Sandi, Yes, condensation on windows is undesirable because it obscures the view, and when it runs down, it deteriorates the window frame. It occurs when warm moisture laden air meets a very cold surface, and the moisture from the air condenses onto the surface. This is why you will also see it on toilet tanks in the summer months, and on cold water pipes in the basement. It is controlled in two ways: (1) Remove as much of the moisture as possible as close to the source as possible, i.e. range hoods with fans that vent outside, exhaust fans in bathrooms, and dehumidifiers in basements. (2) Warm the window surface by using energy efficient windows, or storm windows. This also applies to putting terry covers on toilet tanks, and insulation on pipes in the basement. ...Just some basic theory, but I hope it helps.