A review of recent simulation and experimental studies of the colliding pulse injection scheme is presented. One dimensional particle in cell simulations show that when the colliding pulses have parallel polarizations, the dominant effects that have to be considered for modeling electron injection in plasma waves are (i) stochastic heating and (ii) wakefield inhibition at the collision. With cross polarized pulses, injection of an electron beam is still possible because stochastic heating still occurs. However, it is found numerically that the injection threshold is higher in this case. The simulations also underline the possibility of tuning the electron beam parameters by modifying the injection laser pulse. Experiments (i) validate these scenarios and show that stable and high quality electron beams are produced when two counterpropagating laser pulses collide in an underdense plasma and (ii) confirm very clearly the existence of a threshold for injection, which is higher with cross polarized pulses than with parallel polarized pulses.