  In the context of this dissertation, we study the emergence of black-string
and black-hole solutions in the framework of five-dimensional braneworld
models. The main motivation for studying such theories stems from the
Randall-Sundrum model, which was formulated by Lisa Randall and Raman Sundrum
back in 1999. We investigate thoroughly the physical characteristics of
analytic solutions which concern both black strings and five-dimensional
localized black holes. To be more precise, the black-string solutions emerge in
the context of a five-dimensional scalar-tensor theory, where the brane
line-element is found to describe a Schwarzschild-(anti-)de Sitter spacetime.
The cases of de Sitter, anti-de Sitter and Minkowski branes are examined
separately and in great detail. As far as the five-dimensional black holes are
concerned, at first, we present an "algorithm" that one may use in order to
construct from first principles the geometry of analytic and exponentially
localized five-dimensional braneworld black holes. In each case, the point-like
singularity of the black hole lies entirely on the 3-brane, while its event
horizon is exponentially localized close to the 3-brane thus exhibiting a
pancake shape. In the first case, the induced line-element on the brane assumes
the form of the Schwarzschild solution while the bulk geometry is effectively
AdS$_5$ outside the horizon. In the second case, the induced brane geometry is
described by the Reissner-Nordstr\"{o}m-(A)dS line-element, where a careful
classification of the horizons takes place as well. In both cases, the derived
geometry is supported by an anisotropic fluid in the bulk described only by two
independent components, the energy density and tangential pressure, whereas no
matter needs to be introduced on the brane for its consistent embedding in the
bulk.
