The presence of hydrogen in metallic materials can cause catastrophic early fractures that is known as hydrogen embrittlement. Observing the hydrogen and its associated influences in microstructure has been a grand challenge that limits the development of a solution to this problem. To this end, our research group have developed a special tool, cryogenic atom probe tomography (cryo-APT), for hydrogen mapping and applied it in combination with a micromechanical approach to investigate hydrogen embrittlement in steels. Our efforts have led to new insights for deciphering hydrogen trapping and embrittling mechanisms in steels, facilitating the development of the steel microstructure that has a good resistance to hydrogen embrittlement.