In this chapter, we explore the composition and fabric of unconventional reservoir rocks in order to understand the variations in elastic properties and anisotropy. First, we survey the range of compositions in unconventional basins and develop a simple classification for the various lithofacies. We then discuss each of the constituents of the rock matrix and describe their role in forming the rock fabric at various scales. The next section covers laboratory measurements of elastic properties and anisotropy, beginning with a brief review of methods for obtaining static, dynamic, anisotropic elastic properties. We discuss the variations of elastic properties with composition and fabric in the context of theoretical bounds from simple rock physics models of layered media to develop a physical understanding of microstructural controls on the stiffness of the rock matrix. The final section covers how elastic properties are estimated from geophysical well logs and reservoir-scale seismic studies. We compare field- and lab-derived elastic properties and discuss their applications for understanding the in situ physical properties of unconventional reservoir rocks.