At an abrupt area change, a propagating detonation wave undergoes diffraction. Depending on a number of parameters, the detonation wave can be either quenched (sub-critical regime) or re-initiated (super-critical regime). Detonation diffraction has been studied since the 1950’s but despite six decades of extensive investigations, only semi-empirical models are available to estimate the critical conditions for successful detonation transmission. The present seminar summarizes the results of three recent studies on detonation diffraction and related phenomena. In the first study, spectroscopic models were employed to post-treat the results of two-dimensional numerical simulation of diffracting detonation allowing for a direct comparison with experimental results from the literature. In the second study, both experiments and simulations were conducted using a planar geometry and quantitative assessment of the critical conditions for successful transmission was performed. In addition, simplified models were used to estimate the respective effects of shock front curvature and volumetric expansion on the diffracting detonation re-ignition process. In the third study, an investigation of the chemical kinetics of hydrogen-air mixtures’ ignition under volumetric expansion conditions was performed. Detailed analyses of the energy release rate per reaction, OH radical sensitivity and rate of production were also conducted.