Since the Watergate era, presidential candidates have released several years of tax returns, allowing voters to peer at their financial choices and discern their entanglements. Mitt Romney has upended that tradition this year. He has released only one complete tax return, for 2010, along with an unfinished estimate of his 2011 taxes. What information he did release provides a fuzzy glimpse at a concerted effort to park much of his wealth in overseas tax shelters, suggesting a widespread pattern of tax avoidance unlike that of any previous candidate.