  I present recent work aimed at showing how currently competing theories of
the early universe leave their imprint on the temperature anisotropies of the
CMB radiation. We consider the 3-point correlation function, as well as the
inherent theoretical uncertainties associated with it, for which we derive
explicit analytic formulae. We apply them in the study of non-Gaussian features
that arise on large scales in the framework of both inflationary and
topological defects models. For inflation, we develop a perturbative analysis
for the study of spatial correlations in the inflaton in the context of the
stochastic approach to inflation. We also include an analysis of a particular
geometry, the so-called `collapsed' 3-point function, in the case of post
recombination integrated effects, arising generically whenever the mildly non
linear growth of perturbations is taken into account. We also devote a part of
the thesis to the study of recently proposed analytic models of topological
defects, and implement them in the analysis of both the CMB excess kurtosis
(for cosmic strings) and the CMB collapsed 3-point function and skewness (for
textures). Lastly, we present a study of the CMB anisotropies on the degree
angular scale in the framework of the global texture scenario, and show the
relevant features that arise; among these, the Doppler peaks.
