Anisotropic (nonspherical) metal nanoparticles are of widespread research interest because changing the shape of metals at the nanoscale can provide access to materials with unique optical, electronic, and catalytic properties. This chapter examines recent progress in elucidating and articulating the role halide ions play in seeded growth with particular emphasis on gold nanoparticles. It discusses the effect of halide ions on the anisotropic growth of metal nanocrystals. Although, the chapter mainly focus on gold, nanocrystals of silver, platinum, or palladium are also be included, as their formation has also been reported to be strongly influenced by halides. It reviews several examples where halides have been specifically reported to direct anisotropic growth and discusses whether the presence of halides is strictly necessary for these shapes to occur. Over the past few decades, anisotropic metal nanocrystals have been prepared by a variety of synthetic approaches, which have become increasingly convenient while providing ever more precise control over nanoparticles shape.