Recent results on the probabilities of electronic transitions of diatomic molecules are reviewed. Experimental methods for determining the absolute ($S_e$, $\vert R_e^{mn}\vert^2$, $f_e^{mn}$, $\tau_{nv'}$) and relative probabilities, the systematic classification and analysis of the data, and criteria of the reliability of the recommended values are discussed. The absolute and relative probabilities published up to and including 1977 have been collected and used to obtain recommended (most reliable) values of the band strengths $S_e(r_{v'v''}$) and oscillator strengths $f_e^{mn}$ for more than 200 molecular systems. The experimental lifetimes $\tau_{nv'}$ are analyzed for more than 150 electronically excited states. Most reliable values are recommended for these lifetimes.