  The Planck nominal mission cosmic microwave background (CMB) maps yield
unprecedented constraints on primordial non-Gaussianity (NG). Using three
optimal bispectrum estimators, separable template-fitting (KSW), binned, and
modal, we obtain consistent values for the primordial local, equilateral, and
orthogonal bispectrum amplitudes, quoting as our final result fNL^local=
2.7+/-5.8, fNL^equil= -42+/-75, and fNL^ortho= -25+\-39 (68% CL statistical).
NG is detected in the data; using skew-C_l statistics we find a nonzero
bispectrum from residual point sources, and the ISW-lensing bispectrum at a
level expected in the LambdaCDM scenario. The results are based on
comprehensive cross-validation of these estimators on Gaussian and non-Gaussian
simulations, are stable across component separation techniques, pass an
extensive suite of tests, and are confirmed by skew-C_l, wavelet bispectrum and
Minkowski functional estimators. Beyond estimates of individual shape
amplitudes, we present model-independent, 3-dimensional reconstructions of the
Planck CMB bispectrum and thus derive constraints on early-Universe scenarios
that generate primordial NG, including general single-field models of
inflation, excited initial states (non-Bunch-Davies vacua), and
directionally-dependent vector models. We provide an initial survey of
scale-dependent feature and resonance models. These results bound both general
single-field and multi-field model parameter ranges, such as the speed of
sound, c_s \geq 0.02 (95% CL), in an effective field theory parametrization,
and the curvaton decay fraction r_D \geq 0.15 (95% CL). The Planck data
significantly limit the viable parameter space of the ekpyrotic/cyclic
scenarios. The amplitude of the 4-point function in the local model tauNL <
2800 (95% CL). These constraints represent the highest precision tests to date
of physical mechanisms for the origin of cosmic structure.
