Summary form only given.The concept of quasi-phase matching (QPM) nonlinear optical processes by periodically inverting a material's nonlinear susceptibility (/spl chi//sub 2/) is a familiar one in 1-D: a well known example is periodically-poled lithium niobate LiNbO/sub 3/ (PPLN) which is commonly used for optical frequency conversion applications. A recent proposal has generalised this concept and introduced the notion of a 2-D nonlinear photonic crystal (NPC) in which /spl chi//sub 2/ changes sign periodically across the plane of the sample. Here we report the demonstration of such a 2-D NPC, hexagonally-poled lithium niobate (HEXLN), and describe its fabrication and phase matching characteristics.