  Dynamical electro-weak symmetry breaking is an appealing, strongly-coupled
alternative to the weakly-coupled models based on an elementary scalar field
developing a vacuum expectation value. In the first two sections of this set of
lectures, I summarize the arguments, based on low-energy phenomenology,
supporting walking technicolor as a realistic realization of this idea. This
pedagogical introduction to walking technicolor, and more generally to the
physics of extensions of the standard model, makes extensive use of effective
field theory arguments, symmetries and counting rules. The strongly-coupled
nature of the underlying interactions, and the peculiar quasi-conformal
behavior of the theory, require to use non-perturbative methods in order to
address many fundamental questions within this framework. The recent
development of gauge/gravity dualities provides an ideal set of such
non-perturbative instruments. The remaining two sections illustrate the
potential of these techniques with two technical examples, one within the
bottom-up phenomenological approach to holography in five-dimensions, the other
within a more systematic top-down construction derived from ten-dimensional
type-IIB supergravity.
