Molecules in (or as) electronic devices are attractive because the variety and flexibility inherent in organic chemistry can be harnessed towards a systematic design of electrical properties. Specifically, monolayers of polar molecules introduce a net dipole, which controls surface and interface barriers and enables chemical sensing via dipole modification. Due to the long range of electrostatic phenomena, polar monolayer properties are determined not only by the type of molecules and/or bonding configuration to the substrate, but also by size, (dis-)order, and adsorption patterns within the monolayer. Thus, a comprehensive understanding of polar monolayer characteristics and their influence on electronic devices requires an approach that transcends typical chemical designs, i.e., one that incorporates long-range effects, in addition to short-range effects due to local chemistry. We review and explain the main uses of polar organic monolayers in shaping electronic device properties, with an emphasis on long-range cooperative effects and on the differences between electrical properties of uniform and non-uniform monolayers.