We report the synthesis and self-assembly of azide and amine trimethoxysilanes that result in mixed monolayers on silica. The amine and azide functional groups can be independently reacted with acid chlorides and terminal alkynes, respectively. Consequently, these orthogonally reactive monolayers represent a general starting point for making bifunctional surfaces. Using X-ray photoelectron spectroscopy, we determined the azide/amine surface ratio as well as the reactivity of the azide and amine functional groups in the mixed self-assembled monolayer (SAM). Significantly, the surface azide/amine ratio was much lower than the azide/amine ratio in the self-assembly mixture. After determining the self-assembly mixture composition that would afford 1:1 azide-amine mixed monolayers, we demonstrated their subsequent functionalization. The resulting bifunctional surface has a similar functional group ratio to the azide/amine precursor SAM demonstrating the generality of this approach.