  The engineering of complex software systems is often the result of a highly
collaborative effort. However, collaboration within a multinational enterprise
has an overlooked legal implication when developers collaborate across national
borders: It is taxable. In this article, we discuss the unsolved problem of
taxing collaborative software engineering across borders. We (1) introduce the
reader to the basic principle of international taxation, (2) identify three
main challenges for taxing collaborative software engineering making it a
software engineering problem, and (3) estimate the industrial significance of
cross-border collaboration in modern software engineering by measuring
cross-border code reviews at a multinational software company.
