The initiated chemical vapor deposition (iCVD) technique is an all‐dry method for designing organic and hybrid polymers. Unlike methods utilizing liquids or line‐of‐sight arrival, iCVD provides conformal surface modification over intricate geometries. Uniform, high‐purity, and pinhole‐free iCVD films can be grown with thicknesses ranging from >15 µm to <5 nm. The mild conditions permit damage‐free growth directly onto flexible substrates, 2D materials, and liquids. Novel iCVD polymer morphologies include nanostructured surfaces, nanoporosity, and shaped particles. The well‐established fundamentals of iCVD facilitate the systematic design and optimization of polymers and copolymers. The functional groups provide fine‐tuning of surface energy, surface charge, and responsive behavior. Further reactions of the functional groups in the polymers can yield either surface modification, compositional gradients through the layer thickness, or complete chemical conversion of the bulk film. The iCVD polymers are integrated into multilayer device structures as desired for applications in sensing, electronics, optics, electrochemical energy storage, and biotechnology. For these devices, hybrids offer higher values of refractive index and dielectric constant. Multivinyl monomers typically produce ultrasmooth and pinhole‐free and mechanically deformable layers and robust interfaces which are especially promising for electronic skins and wearable optoelectronics. Using initiated chemical vapor deposition (iCVD), organic and hybrid thin films can form directly on substrates of virtually any composition and geometry. Free‐radical polymerization of adsorbed monomers is initiated by vapor phase radicals formed by thermal decomposition. The established fundamentals enable the rational optimization of iCVD polymers and copolymers for sensing, optoelectronics, electrochemical energy storage, and biotechnology.