Multi-state taxation refers to the situation where an individual or business entity is subject to income tax in more than one state. This typically occurs when someone earns income from sources in multiple states or resides in one state but works in another. The IRS provides guidance on how to handle multi-state taxation, including allocating income, claiming credits or deductions, and filing requirements. Proper documentation and adherence to each state’s tax laws are crucial to avoid double taxation or penalties.