The β-NMR technique and its application to the study of materials science are introduced. Using some different types of accelerator facility, β-NMR probe nuclei for various elements are useful as a beam with wide energy range, which enables us to select an implantation depth into a sample from surface to bulk. Our recent β-NMR studies on ⁸Li in Li ion conductor material Li₇La₃Zr₂O₁₂ and ¹²N in H₂O are presented.