Within the past four years, experiments with high power, high frequency radio waves have proved the feasibility of temporarily altering the ionosphere's properties. Many different radio and photometric effects have been observed as a result of the ionospheric modification. This paper provides a survey of some of the effects observed with vertical incidence radio techniques when the US Department of Commerce's Platteville facility, near Boulder, Colorado, is used to illuminate the overhead ionosphere with an equivalent isotropically radiated power of the order of 100 Mw. A variety of different and repeatable phenomena are observed to occur in the F region. A few always occur; for others, apparently, certain ionospheric conditions must exist. E-region effects observed by these techniques are small, but substantial effects are noted in the D region.