The synthesis of gold nanoparticles (Au NPs) capped by poly(1-vinylpyrrolidin-2-one (PVP, average M over bar w= 10 000 kDa) yields moderately dispersed (6-8.5 nm) product with limited morphological control while larger NPs (15-20 nm) are reliably prepared using trisodium citrate (Na(3)Cit) as a reductant/capping agent. Excellent size control in the intermediate 10 nm regime is achieved by hybridizing these methodologies, with highly monodisperse, polycrystalline Au NPs forming. For a Na(3)Cit:PVP:Au ratio of 3.5:3.5:1, anisotropic NPs with an aspect ratio of 1.8:1 suggest the systematic agglomeration of NP pairs. Enhanced control of NP morphology is allowed by the 1,2-tetradecanediol reduction of Au-III in the presence of straight chain, molecular anti-agglomerants. Last, ligand substitution is used to controllably grow preformed Au seeds. In spite of the extended growth phase used, the replacement of phosphine by 1-pentadecylamine affords highly monodisperse, cuboidal NPs containing a single clearly visible twinning plane. The allowance of particle growth parallel to this close-packed plane explains the remarkable particle morphology.