  This course is an introduction to the physics of braneworlds. We concentrate
on braneworlds with only one extra-dimension and discuss their gravity. We
derive the gravitational equations on the brane from the bulk Einstein equation
and explore some limits in which they reduce to 4-dimensional Einstein gravity.
We indicate how cosmological perturbations from braneworlds are probably very
different from usual cosmological perturbations and give some examples of the
preliminary results in this active field of research. For completeness, we also
present an introduction to 4-dimensional cosmological perturbation theory and,
especially its application to the anisotropies of the cosmic microwave
background.
