The "ceiling principle", devised by the National Research Council, provides an even more conservative estimate of the likelihood of occurrence of a DNA profile than the fixed-bin or floating-bin methods currently used by the forensic community. The TWGDAM does not recommended the ceiling principle because its use is based on the faulty premise that there is more genetic variation among subgroups within a major population group than between major population groups. Extant data demonstrate the opposite conclusion and that the application of the ceiling principle is unnecessary. Methods currently used by forensic scientists have been shown to be robust scientifically. For those courts that still prefer DNA profile frequency estimates based on the conservative interim ceiling principle approach, TWGDAM has developed a consensus approach for the ceiling principle. There are two basic approaches to establishing ceiling principle frequencies. These are based on using either fixed or floating bins to assign allele frequencies. Since both the fixed-bin and floating-bin ceiling principle approaches, which are described in this article, yield similar DNA profile frequency estimates, either can be used. It is unnecessary to provide estimates for both approaches. The choice is up to the laboratory. 36 references