A major aspect of hetero-interfaces is the relative position the energy levels / bands of two adjacent phases, known as the ‘injection barrier’. From inorganic semiconductors to thin organic films, interfacial energy alignment is accompanied by charge redistribution and therefore, creation of a built-in potential. Seemingly, adsorbed molecules (isolated or within a monolayer) follow similar principles: the injection barrier is equivalent to the tunneling barrier in molecular junctions (ε, all quantities are illustrated below) while charging is expressed as an adsorption-induced molecular dipole (Δ). However, molecules have no free carriers and their nearest energy level is way-off the electrode’s Fermi-level. This explains why the electrode-molecule interface is widely assumed to be ‘inert’: adsorption induces no long-range charge rearrangement beyond the mere chemical bond (Δ=0; left-side illustration). This scenario is equivalent to ‘vacuum level alignment’ (Schottky limit) in bulk semiconductors where the injection (tunneling) barrier is predicted from the work-function of the clean electrode (WF) and the frontier-level of the isolated molecule (IP in the illustration). However, evidence is growing for the opposite: electrodes of largely different work-function hardly affect the tunneling barrier (constant ε) while the molecular dipole varies drastically (Δ ≠ 0; right-side illustration). It is as if the molecules are “Fermi-level-pinned”, but molecules have no Fermi level! Instead the electrochemical potential (μ) of the molecule is a well-defined thermodynamic quantity. I will describe how electrochemical balance combined with the notion of chemical “hardness / softness” (electronic polarizability) provide qualitative guidelines for predicting the energy alignment of adsorbed molecules. This concept will be demonstrated on our own results with molecular monolayers on Si(111) and by reference to literature works on thiol-bonded monolayers on Au.