  We have imaged the ejecta of GK Persei (Nova Persei 1901 A.D.) with the
Hubble Space Telescope (HST), revealing hundreds of cometary-like structures.
One or both ends of the structures often show a brightness enhancement relative
to the structures' middle sections, but there is no simple regularity to their
morphologies (in contrast with the Helix nebula). Some of the structures'
morphologies suggest the presence of slow-moving or stationary material with
which the ejecta is colliding, while others suggest shaping from a wind
emanating from GK Per itself. A detailed expansion map of the nova's ejecta was
created by comparing HST images taken in successive years. WFPC2 narrowband
images and STIS spectra demonstrate that the physical conditions in the ejecta
vary strongly on spatial scales much smaller than those of the ejecta. Directly
measuring accurate densities and compositions, and hence masses of this and
other nova shells, will demand data at least as resolved spatially as those
presented here. The filling factor the ejecta is < 1%, and the nova ejecta mass
must be less than $10^{-4} \Msun$. A few of the nebulosities vary in brightness
by up to a factor of two on timescales of one year. Finally, we present the
deepest images yet obtained of a jet-like feature outside the main body of GK
Per nebulosity, and the first spectrum of that feature. Dominated by strong,
narrow emission lines of [NII], [OII], [OIII], and [SII], this feature is
probably a shock due to ejected material running into stationary ISM, slowly
moving ejecta from a previous nova episode, or circum-binary matter present
before 1901. An upper limit to the mass of the jet is of order a few times
$10^{-6} \Msun$. The jet might be an important, or even dominant mass sink from
the binary system. The jet's faintness suggests that similar features could
easily have been missed in other cataclysmic binaries.
