A key defense against corrosion in passive metals, such as stainless steels (SS), is the formation of a nanometer-thick oxide/hydroxide layer. Modern structure-sensitive techniques such as scanning tunneling microscopy (STM), atomic force microscopy (AFM), and X-ray diffraction (XRD) at grazing incidence using synchrotron radiation reveal that films on passive metals are predominantly crystalline. Even if not initially crystalline upon formation, these films often transition to a crystalline state over time, developing into multilayer structures with thicknesses ranging from 0.1 to 5 nm. Growth kinetics models explain the dissolution of the underlying passive metal as a process of cation transfer through the solid crystalline phase. This cation transport is markedly accelerated at defective regions, such as oxide and metal grain boundaries, inclusions and second phase particles, and atomic defects in crystalline oxide structures etc. These imperfections can cause localized thinning of the passive layer, particularly in solutions containing Cl -or other halides, leading to film breakdown and accelerated localized dissolution or pitting corrosion. It should be emphasized that not every defect leads to pit formation, and there is currently no reliable method to predict which defects will result in pit development, making the process appear random and often described using stochastic rather than deterministic models. A promising approach to address this issue involves the use of in-situ opto-electrochemical microscopy, where the optical image of the corroded interface is directly correlated with the global electrochemical outputs. As of now, the most commonly derived information from this method is the identification of pit locations, based on the appearance of low-contrast regions in optical images. Despite its simplicity, this approach has already offered unique insights into the mechanism of pit formation. It directly demonstrated that, although the initial appearance of primary pits is random, the formation of subsequent pits follows a probabilistic pattern governed by stochastic rules, often influenced by the position of the primary pits. These observations have been explained by the concept of communication between closely spaced pits, enabled by the exchange of matter (driven by concentration gradients) and electrochemical current (driven by electric field gradients).