  An electromagnetic wave-packet propagating in a linear, homogeneous, and
isotropic medium changes shape while its envelope travels with different
velocities at different points in spacetime. In general, a wave-packet can be
described as a superposition of plane-waves having different frequencies
{\omega} and different propagation vectors k. While the angular spread of the
k-vectors gives rise to diffractive effects, it is the frequency-dependence of
the refractive index of the host medium that is commonly associated with
optical dispersion. When the spectral distribution of the wave-packet is
confined to a narrow band of frequencies, and also when the spread of the
k-vectors is not too broad, it is possible, under certain circumstances, to
obtain analytical expressions for the local and/or global trajectory of the
packet's envelope as it evolves in time. This paper is an attempt at a
systematic description of the underlying physical assumptions and mathematical
arguments leading to certain well-known properties of narrowband
electromagnetic wave-packets in the presence of diffractive as well as
(temporally) dispersive effects.
