This module reviews selected constitutional principles and judicial decisions that inform state income tax nexus standards. Participants examine traditional and alternative apportionment factor formulas, including variations in sales factor weighting, and explore sourcing methodologies such as market-based sourcing and cost of performance. Through computational examples and a client case study, participants calculate state apportionment percentages using statutory approaches. The program also addresses the state-level treatment of pass-through entity (PTE) taxes and incorporates research and group discussion activities to reinforce key concepts.