The main interjurisdictional issues in the context of federal countries are: 

a. Dividing the VAT tax base among the jurisdictions while avoiding overlapping and underlapping. 

b. Collecting the tax when transactions in goods and services cross borders. 

c. Coordinating definitions, rates, and administration among states and between a tax at the national level and corresponding taxes at the state level. Is there a model solution for these issues for all federal countries? If so, what is it; if not, why not and what range of solutions exists? What other important interjurisdictional issues must federations face?