The meaning and utility of three principles of uncertainty is discusse
d. These principles, which are referred to as a principle of minimum u
ncertainty, a principle of maximum uncertainty, and a principle of unc
ertainty invariance, depend on the theory in which uncertainty is conc
eptualized. Due to a connection between uncertainty and information, t
he principles may also be conceived as principles of information. To m
ake the principles operational in a particular uncertainty theory, we
need to measure the amount of relevant uncertainty (and associated inf
ormation) in each problem situation describable within the theory. Wel
l-justified measures of uncertainty have thus far been established onl
y in some uncertainty theories. These theories, their uncertainty meas
ures, and the associated uncertainty principles are overviewed in the
paper.