Modelling Inhomogeneity in the Universe
  An overview of some recent developments in inhomogeneous models is presented.
As the volume and precision of cosmological data improves, it will become more
and more essential to understand the non-linear behaviour of the Einstein field
equations. This requires the study of exact inhomogeneous solutions, including
their density distributions, their evolution, their geometry, and their causal
structure. Observations are strongly affected by the detailed geometry and
evolution of a model, and therefore interpretation of observations depends on
understanding them.
  It is generally assumed the universe is homogeneous if averaged over large
enough scales, but to actually prove this is so, will require the assumption to
be relaxed, and a rigorous inhomogeneous approach to be applied. Though the \LT
metric has long been used for models of spherical inhomogeneities, there have
been a number of new results, including a variety of methods for creating
models with specific properties, and their application to cosmic structures on
several different scales. Interest in the Szekeres metrics is on the increase,
and the quasi-spherical metric was recently used to model specific cosmic
structures for the first time. The quasi-planar and quasi-hyperspherical
metrics have been hardly studied until recent work invesigated their physical
and geometric properties. There is enormous scope for work with these metrics.
