  We investigate cosmological consequences arising from the interaction between
a homogeneous and isotropic brane-universe and the bulk. A Friedmann equation
is derived which incorporates both the brane and bulk matter contributions,
which are both assumed to be of arbitrary fluid form. In particular, new terms
arise which describe the energy flow onto (or away from) the brane, as well as
changes of the equation of state in the bulk. We discuss Randall-Sundrum type
models as well as dilatonic domain walls and carefully consider the conditions
for stabilising the induced gravitational constant. Furthermore, consequences
for cosmological perturbations are analysed. We show that, in general,
super-horizon amplitudes are not constant.
