The growth of monolayers is studied in more detail with the help of methods with atomic resolution. Techniques like scanning tunneling microscopy provide direct images of growing films showing nucleation, shape and growth defects of monoatomic or larger islands. Quantitative informations on average sizes and size distributions are derived from spot profile analysis of any diffraction spot at any temperature during growth in real time. Especially spot profile analysis of low energy electron diffraction (SPA-LEED) is well developed. Many informations are available for semiconductor systems (like Si on Si or Ge on Si) and metal films (like Pb on Cu or Ag on Si), which reveal the wide range of growth modes depending on many parameters like material, temperature, deposition rates or defects.