The Wolfenstein matter effect significantly alters neutrino flavor transformations in matter. This effect is responsible for the 1/3 reduction in the solar electron neutrino flux observed by Davis and also has significant effects in terrestrial oscillation experiments such as T2K, NOvA, DUNE and T2HK/K. In this seminar I will present some recent results on 3 (& beyond) flavor matter effects for long baseline experiments.