People read more slowly from CRT displays than from paper (see, for example, Gould and Grischkowsky, 1984). This report summarizes ten experiments and several more analyses that seek to explain the cause of this reading-speed difference. Typically, each experiment isolates one variable and studies whether it explains the difference. Results show that no one variable studied (e. g. , experience in using CRT displays; display orientation; character size; font; or polarity) explains it. The tentative conclusion is that the difference is due to a combination of variables, probably centering on the image quality of the characters themselves.