This book includes two topics. Part 1 is on atom-photon interactions without the rotating-wave approximation (RWA), including the Lamb shift, the quantum Zeno and anti-Zeno effect, the polarizability, the superradiance and the subradiance. We go beyond the RWA with a unitary transformation. After the transformation, the Hamiltonian only has rotating-wave terms. The effects of the counter rotating terms include a level shift and a modification factor of the rotating-wave terms. Part 2 is on the reflection and the transmission in a standing wave coupled electromagnetically induced transparency (SWEIT) system of both cold and hot atoms. We treat the SWEIT system with the wave-mixing method. Infinite quantum paths are calculated with continued fractions. An optical diode is made by detuning the two components of the standing wave, which breaks the time reversal symmetry and forms a moving photonic crystal.