  We searched for dust or debris rings in the Pluto-Charon system before,
during, and after the New Horizons encounter. Methodologies included searching
for back-scattered light during the approach to Pluto (phase $\sim15^\circ$),
in situ detection of impacting particles, a search for stellar occultations
near the time of closest approach, and by forward-scattered light during
departure (phase $\sim165^\circ$). A search using HST prior to the encounter
also contributed to the results. No rings, debris, or dust features were
observed, but our detection limits provide an improved picture of the
environment throughout the Pluto-Charon system. Searches for rings in
back-scattered light covered 35,000-250,000 km from the system barycenter, a
zone that starts interior to the orbit of Styx, and extends to four times the
orbital radius of Hydra. We obtained our firmest limits using the NH LORRI
camera in the inner half of this region. Our limits on the normal $I/F$ of an
unseen ring depends on the radial scale of the rings: $2\times10^{-8}$
($3\sigma$) for 1500 km wide rings, $1\times10^{-8}$ for 6000 km rings, and
$7\times10^{-9}$ for 12,000 km rings. Beyond $\sim100,000$ km from Pluto, HST
observations limit normal $I/F$ to $\sim8\times10^{-8}$. Searches for dust from
forward-scattered light extended from the surface of Pluto to the Pluto-Charon
Hill sphere ($r_{\rm Hill}=6.4\times10^6$ km). No evidence for rings or dust
was detected to normal $I/F$ limits of $\sim8.9\times10^{-7}$ on $\sim10^4$ km
scales. Four occulation observations also probed the space interior to Hydra,
but again no dust or debris was detected. Elsewhere in the solar system, small
moons commonly share their orbits with faint dust rings. Our results suggest
that small grains are quickly lost from the system due to solar radiation
pressure, whereas larger particles are unstable due to perturbations by the
known moons.
