Monolayers have a multitude of applications both at the air-water and at air-solid interphases.
Nanoparticle monolayers can be used to create functional surfaces that have for instance anti-reflective or superhydrophobic properties.
Monolayers are frequently encountered in biology. A micelle is a monolayer, and the phospholipid lipid bilayer structure of biological membranes is technically two monolayers. Langmuir monolayers are commonly used to mimic cell membrane to study the effects of pharmaceuticals or toxins.