The internal structure of as-deposited, high grafting density, ultrathin (thickness < 25 lint) diblock copolynier brushes (DCBs) is resolved using neutron reflectivity (NR) and grazing incidence small-ray scattering (GISAXS) DCBs of various thicknesses containing deuterated polystyrene (dPS) angle X-ray scattering (GISAXS) DCBs of various thicknesses contianing deuterated polystrene (dPS) blocksand poly(methyl acrylate) (PMA) blocks with dPS (dPS-b-PMA) or with PMA(PMA-b-dPS)adajacent to the substrate were synthesized by atom transfer radical polymcrization (ATRP) For the th.nnest films, it model of two layers With a smooth interfacial gradient provides it good description of the data For thicker dPS-b-PMA samples of sufficiently asymmetric compostion, a third layer must be included. This is consistent with the presence of lateral ordering in the center of the brush, its evidenced by GISAXS data. For the thinnest DCBs, the gradient in composition perpendicular to the surface extends through nearly the entire thickness of the brush, consistent with the conjecture that the gradient is Imposed by the presence of the surface field and tethering oil it material that, in the absence of tethering, would be disordcred The Interface widths for brushes with it PMA block tethered 10 the Substrate are smaller than for brushes with a dPS block tethered to the substrate. In general. the region adjacent to the Substrate is found to have a substantial composition of the "top" block in contrast to expectations from theory Experimental interface width values me consistent with expectations from self-consistent Field theory for brushes with a dPS bottom block A scaling theory for the interfacial width in a DCB identifiesa crossover as (d/R-g)(2) > chi N frorn the classical Helfand-Tagami regime, where w approximate to/(chi(1/2)), to a new stretched interface regime, where w approximate to d/(chi N). The scaling theory provides insight into how interface width in the DCBs should vary with grafting density, interaction pdrarricter, and chain molecular weight and is qualitatively consistent with the experimental data and suggests directions for further work