Simplified cost-scaling relationships are employed to identify the key economic drivers for fusion power systems. These economic drivers are examined in the context of compact reactor design trends. On the basis of this examination, four areas are identified as being critical paths in the development of compact designs. Two areas are physics in nature and concept dependent. These are the scaling dependence of energy confinement and the limitations on beta. Two areas are technological in nature and generic. These are the development of first-wall materials capable of operating at high wall loading (>5 MW/m2) and with useful lifetimes (∼1 yr) and maintenance approaches compatible with high availability and first-wall replacement times of ∼1 yr.