The formation of self-assembled two dimensional structures at the solid-solution interface has long been treated as an equilibrium process.  In the case of porphyrin adsorption this is seldom true with kinetics often determining the structures observed at temperatures below about 50°C.  Using scanning tunneling microscopy (STM) we will demonstrate that molecular scale time evolution studies coupled with concentration variations are essential for determining the extent to which thermodynamics or kinetics control the observed surface structure.  Examples will be given of system in thermodynamic equilibrium and of those where kinetics is controlling.  We also will demonstrate how coadsorption of two species with very different desorption rates can produce new 2D structures.  An interesting example of cooperative adsorption will also be presented.