  We examine the dynamical implications of an interaction between some of the
fluid components of the universe. We consider the combination of three matter
components, one of which is a perfect fluid and the other two are interacting.
The interaction term generalizes the cases found in scalar field cosmologies
with an exponential potential. We find that attracting scaling solutions are
obtained in several regions of parameter space, that oscillating behaviour is
possible, and that new curvature scaling solutions exist. We also discuss the
inflationary behaviour of the solutions and present some of the constraints on
the strength of the coupling, namely those arising from nucleosynthesis.

General Relativity and Quantum Cosmology