Anisotropic nanoparticles (NPs) exhibit unique and superior physicochemical properties to isotropic particles. This chapter illustrates the breadth of hierarchically porous and anisotropic NPs and approaches to their synthesis and catalytic applications, focusing on the impact of NP morphology, porosity, and chemical functionalization on activity, selectivity, and stability. Top-down approaches create NPs by the removal of extraneous material from a bulk sample using reactive ion or chemical etching to produce highly uniform NPs. In the bottom-up approach, molecular components arrange into more complex assemblies atom by atom, molecule by molecule, or cluster by cluster. Catalytic Janus nanostructures include bimetallics, metals and oxides, and inorganic carbons and oxides. The coupling of two or more distinct pore networks, typically micro-and mesopores or meso-and macropores, yields material possessing hierarchical porosity. Such architectures have shown benefits in a variety of catalytic transformations, often attributed to enhanced internal mass transport and/or superior dispersion of active sites.