A catalytic wall-flow monolith filter having three-way catalytic activity for use in an emission treatment system of a positive ignition internal combustion engine, wherein the wall-flow monolith filter comprises a porous filter substrate, the porous filter substrate having a first face and a second face defining a longitudinal direction therebetween and first and second pluralities of channels (5, 6) extending in the longitudinal direction, wherein the first plurality of channels is open at the first face and closed at the second face and the channels of the first plurality of channels are defined in part by channel wall surfaces, wherein the second plurality of channels is open at the second face and closed at the first face and the channels of the second plurality of channels are defined in part by channel wall surfaces and wherein channel walls between the channel wall surfaces of the first plurality of channels and the channel wall surfaces of the second plurality of channels are porous, wherein a first on-wall coating comprising catalytic material having a layer thickness is present on at least the channel wall surfaces of the first plurality of channels, wherein the catalytic material on channel wall surfaces of the first plurality of channels comprises one or more platinum group metal selected from the group consisting of (i) rhodium (Rh) only; (ii) palladium (Pd) only; (iii) platinum (Pt) and rhodium (Rh); (iv) palladium (Pd) and rhodium (Rh); and (v) platinum (Pt), palladium (Pd) and rhodium (Rh) and a refractory metal oxide support, wherein: the layer thickness of the on-wall coating present on channel wall surfaces of the first plurality of channels varies continually along the longitudinal direction, wherein an on-wall coating comprising catalytic material having a layer thickness is further provided on the wall surfaces of the second plurality of channels, wherein an on-wall coating comprising catalytic material having a layer thickness is present on the channel wall surfaces of the second plurality of channels, wherein the catalytic material on channel wall surfaces of the second plurality of channels comprises one or more platinum group metal selected from the group consisting of (i) rhodium (Rh) only; (ii) palladium (Pd) only; (iii) platinum (Pt) and rhodium (Rh); (iv) palladium (Pd) and rhodium (Rh); and (v) platinum (Pt), palladium (Pd) and rhodium (Rh) and a refractory metal oxide support, wherein the layer thickness of the on-wall coating present on channel wall surfaces of the second plurality of channels varies continually along the longitudinal direction, wherein a maximum layer thickness present on channel wall surfaces of the first plurality of channels is at the open end of the first plurality of channels, wherein a maximum layer thickness present on channel wall surfaces of the second plurality of channels is at the open end of the second plurality of channels. the layer thickness of the on-wall coating present on channel wall surfaces of the first plurality of channels varies continually along the longitudinal direction, wherein an on-wall coating comprising catalytic material having a layer thickness is further provided on the wall surfaces of the second plurality of channels, wherein an on-wall coating comprising catalytic material having a layer thickness is present on the channel wall surfaces of the second plurality of channels, wherein the catalytic material on channel wall surfaces of the second plurality of channels comprises one or more platinum group metal selected from the group consisting of (i) rhodium (Rh) only; (ii) palladium (Pd) only; (iii) platinum (Pt) and rhodium (Rh); (iv) palladium (Pd) and rhodium (Rh); and (v) platinum (Pt), palladium (Pd) and rhodium (Rh) and a refractory metal oxide support, wherein the layer thickness of the on-wall coating present on channel wall surfaces of the second plurality of channels varies continually along the longitudinal direction, wherein a maximum layer thickness present on channel wall surfaces of the first plurality of channels is at the open end of the first plurality of channels, wherein a maximum layer thickness present on channel wall surfaces of the second plurality of channels is at the open end of the second plurality of channels.