Introduction: Let me introduce ECP and TLM-PSD. What makes the advent of ECP? Porous materials have been widely used in various scientific and industrial applications. They have attracted special concerns as electrodes used in electrochemical energy storage devices such as electrochemical capacitors, batteries and fuel cells. Understanding of the microstructure of a porous electrode is essential since the structure affects the electrochemical properties of the electrode and thus the performance of the device. Various techniques are available to analyze the microstructure of porous materials: gas adsorption, He pycnometry, mercury intrusion porosimetry, SEM, X-ray diffraction and so on. Each technique has its own merits and demerits. For example, the nitrogen adsorption technique is difficult to detect pores larger than 100 nm. Mercury porosimetry is inapplicable to soft materials since its operation at high pressure leads to the deformation of pore structure. Most of all, they are non in situ techniques so that measured pores or surfaces may not be identical to those accessible to electrolyte ions. We have developed a novel analytical method, electrochemical porosimetry, by which the geometric parameters meaningful in electrochemical systems can be obtained in situ. This method can analyze microstructures of a wide spectrum of porous materials used in various fields. The methodology is based on the transmission line model with pore size distribution (TLM-PSD) that relates electrochemical impedance data with microstructural information. Pore length, as well as pore size distribution, can be obtained by fitting the TLM-PSD to the experimental impedance data of a porous electrode. This geometric information was validated for the microporous, mesoporous and macroporous samples by comparing with the data obtained from conventional porosimetry. Also, the electrochemical porosimetry could be used as a nondestructive probe to investigate the construction of electrochemical devices.