TCSFA is Trajectory-based Coulomb-corrected Strong Field Approximation. It incorporates long-range Coulomb effects into the well-known theoretical framework of strong field approximation (SFA) established during 1960s by Keldysh. Compared with many other varieties taking binding potential into consideration, the TCSFA is developed in terms of the conceptually simple "quantum orbits", akin to the method of Feynman's path integrals. This method provides a powerful theoretical tool to analyze momentum spectra for strong field ionization of photo-electron(s) in the unperturbative domain.