This Article provides a comprehensive analysis of state constitutional limits on legislative incorporation of dynamic federal law, as occurs when a state legislature incorporates future federal tax, environmental or health laws. Many state judicial decisions draw on the nondelegation doctrine to endorse an ex ante prohibition on state legislative incorporation of dynamic federal law. However, the analysis in this Article shows how bedrock principles related to separation of powers under state constitutions, such as protecting transparency, reinforcing accountability, and protecting against arbitrariness in lawmaking, are not consistent with this approach. Instead, this Article highlights two practices that can make dynamic incorporation of federal law more compatible with state separation of powers: a) accountable intermediaries, such as administrative agencies, as a was of preserving political accountability with incorporation of dynamic federal sources of law; and b) ex post judicial review, as a mechanism to provide standards and safeguards to protect against arbitrariness in lawmaking. The analysis highlights serious flaws with judicial interpretations of state constitutions that impose an ex ante barrier to the adoption of dynamic federal law. It also advances “hard look federalism” as a novel approach to judicial review by state appellate courts that can allow states to both protect their own separation of powers concerns and improve the operation of federalism, particular by enhancing state participation in adoption, interpretation, and implementation of federal standards.