  The trace anomaly of conformal field theories in four dimensions is
characterized by '$a$' and '$c$'-functions. The scaling properties of the
effective action of a CFT in the presence of boundaries is shown to be
determined by $a$, $c$ and two new functions (charges) related to boundary
effects. The boundary charges are computed for different theories and different
boundary conditions. One of the boundary charges depends on the bulk $c$
charge.
