An in situ measurement means a collection of physical or chemical properties of materials at the given sample environments such as temperature, pressure, electric/magnetic field, stress, pH, light and so on. An in operando measurement looks similar to the case of in situ measurement but is distingushed from that since it was coined as a contineous collection of data under normal working condition (i.e. catalytic reaction). Gas (H₂, CH₄, CO₂, etc.) sorption/desorption, structural phase transition, charge/discharge of battery, photosynthetic process, catalytic reactions can be observed in atomic scale by neutron and X-ray scattering experiments. By the virtue of bright X-ray source and high throughput detection technology, time evolving physico-chemical phenomena can be investigated. Especially, neutron can discriminatively probe the behaviors of light elements such as H, Li, C, N, O among heavy elements and thus its application to the energy materials is gradually incresed. Experimental details and results from recent in situ and in operando neutron/X-ray experiments on hydrogen storage mechanism and catalytic hydrogenation mechanism will be introduced.