  The Planck full mission cosmic microwave background(CMB) temperature and
E-mode polarization maps are analysed to obtain constraints on primordial
non-Gaussianity(NG). Using three classes of optimal bispectrum estimators -
separable template-fitting (KSW), binned, and modal - we obtain consistent
values for the local, equilateral, and orthogonal bispectrum amplitudes,
quoting as our final result from temperature alone fNL^local=2.5+\-5.7,
fNL^equil=-16+\-70 and fNL^ortho=-34+\-33(68%CL). Combining temperature and
polarization data we obtain fNL^local=0.8+\-5.0, fNL^equil=-4+\-43 and
fNL^ortho=-26+\-21 (68%CL). The results are based on cross-validation of these
estimators on simulations, are stable across component separation techniques,
pass an extensive suite of tests, and are consistent with Minkowski functionals
based measurements. The effect of time-domain de-glitching systematics on the
bispectrum is negligible. In spite of these test outcomes we conservatively
label the results including polarization data as preliminary, owing to a known
mismatch of the noise model in simulations and the data. Beyond fNL estimates,
we present model-independent reconstructions of the CMB bispectrum and derive
constraints on early universe scenarios that generate NG, including general
single-field and axion inflation, initial state modifications, parity-violating
tensor bispectra, and directionally dependent vector models. We also present a
wide survey of scale-dependent oscillatory bispectra, and we look for
isocurvature NG. Our constraint on the local primordial trispectrum amplitude
is gNL^local=(-9.0+\-7.7)x10^4 (68%CL), and we perform an analysis of
additional trispectrum shapes. The global picture is one of consistency with
the premises of the LambdaCDM cosmology, namely that the structure we observe
today was sourced by adiabatic, passive, Gaussian, and primordial seed
perturbations.[abridged]

Cosmology and Nongalactic Astrophysics