We present an examination of the H + HX→ H2+Xand H + HX→ HX+ H (X= Cl, Br, I) reactions as a case study of the kind of detailed dynamical information that can be provided by combining thorough experimental measurements with extensive theoretical (computational) simulations. The experimental component is state-to-state dynamics measurement of the absolute cross-sections for reaction from specific quantum states of the HXreactant molecule to particular quantum states of the H2and HXproduct molecules. The interpretation of the quite detailed experimental results is provided by the theoretical component of this work, computational simulations of the reaction dynamics using quasi-classical trajectory calculations. Testing and validation of the quasi-classical trajectory calculations is done by comparison of the state-to-state dynamics theoretically predicted with the dynamics actually revealed in the experiments. When the trajectory calculations are so validated they are used to explore aspects of the dynamics not accessible experimentally and to develop physical models that promote understanding of the dynamics.