Small strain shear modulus (G0) or the associated shear wave velocity (Vs) is a basic soil property with clear physical meaning, and has a wide range of applications in geotechnical engineering. While it has been extensively studied in the past decades, some aspects of this property are not yet completely understood, due primarily to the particulate nature of soils. The characteristics of individual grains can significantly affect the packing pattern and the grain-to-grain interactions, and hence the overall mechanical properties. This paper presents selected results and findings yielded from a long-term research program which was aimed at understanding the roles played by grain attributes in the small strain stiffness of granular soils. Focus is here placed on grain shape, surface roughness, fines, and the fabric.