2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/54670We consider the actions for ten--dimensional $p$--branes and $D$--branes in an arbitrary curved background and discuss some of their properties. We comment on how the $SL(2,R)$ duality symmetry acts on the five--brane actions.4 pages, latex, uses sprocl.sty; talk given at the Second International Sakharov Conference on Physics (Moscow, May 1996)High Energy Physics - Theorytext