Fabrication of multifunctional surfaces with complexity approaching that found in nature requires the application of a modular approach to surface engineering. We describe a versatile post-polymerization modification strategy to synthesize multifunctional polymer brush surfaces via combination of surface-initiated photopolymerization (SIP) and orthogonal thiol-click reactions. Specifically, we demonstrate two routes to multifunctional brush surfaces: in the first approach, alkyne-functionalized homopolymer brushes are modified with multiple thiols via a statistical, radical-mediated thiol-yne co-click reaction; and in the second approach, statistical copolymer brushes carrying two distinctly-addressable reactive moieties are sequentially modified via orthogonal base-catalyzed thiol-X (where X represents an isocyanate, epoxy, or α-bromoester) and radical-mediated thiol-yne reactions. In both cases, we show that surface properties, in the form of wettability, can be easily tuned over a wide range by judicious choice of brush composition and thiol functionality.