The precise determination of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements Vud and Vus constitutes an important component of the precision test of the Standard Model (SM) and the search for new physics beyond its coverage. In recent years, there has been a resurgence of interest in these matrix elements due to the emergence of a number of intriguing tensions at the 3-sigma level. In this talk I will discuss our current theoretical understanding of the superallowed nuclear beta decay, which is the main avenue for the Vud extraction.