Reactive “polymer nanosheets” consisting of N-dodecylacrylamide and a photocrosslinkable methacryloyl group in the polymer monolayer have been deposited onto solid substrates by the Langmuir–Blodgett technique. The polymer nanosheets have well-ordered molecular alignment and a controlled thickness on the nanoscale. Multiple photopatterning allows the formation of 3D nanostructures, such as pyramids, tracery patterns, etc. (see Figure), with nanometer thickness precision. The scale bar in the bottom figure represents 5.0 mm.