A process is disclosed for producing an alkylaromatic compound in a multistage reaction system comprising at least first and second series-connected alkylation reaction zones, each containing an alkylation catalyst. A first feed comprising an alkylatable aromatic compound and a second feed comprising an alkene are introduced into the first alkylation reaction zone. The first and second alkylation reaction zones are operated under conditions of temperature and pressure effective to cause alkylation of the aromatic compound with the alkene in the presence of the alkylation catalyst, the temperature and pressure being such that the aromatic compound is at least partly in the liquid phase. The alkylation catalyst in the first alkylation reaction zone, which may be a reactor guard bed, has more acid sites per unit volume of catalyst than the alkylation catalyst in the second reaction zone.