  Electromagnetism would be a ``more unified'' theory if there were elementary
magnetic monopoles and/or particles with both electric and magnetic charges
(dyons). I discuss the simplest possibilities for the addition of these
entities onto the Standard Model, and their empirical consequences. Lower
limits on the masses of monopoles and dyons stemming from their quantum effects
on current observables turn out to be much stronger than the existing limits
from direct searches. Anomalies in the three-photon decay of the $Z$ constitute
good specific signatures for monopoles or dyons. $T$-odd observables in the
$e^+e^-\!\rightarrow\! W^+W^-$ process are signatures for dyons, but they are
severely constrained by existing data. The subjects of monopolium, monopole
cosmology and non-elementary monopoles are also discussed.
