Pence in September released a decade's worth of tax returns. Democratic presidential nominee Hillary Clinton and her running mate, Virginia Sen. Tim Kaine, have released nearly 10 years of tax returns.
The Tax History Project compiles tax information from former presidents and recent presidential candidates. The Project lists tax information for all Republican presidential nominees over the past nine elections with the exception of Bob Dole. A 1996 article from the New York Times shows Dole released his tax returns as well.
Presidential nominees are not required to release tax information.
According to the Sunlight Foundation, a nonprofit organization focused on government transparency, tax returns can provide insight into a candidate's values and spotlight his or her potential conflicts of interest.
"There is a reason why banks use tax returns when evaluating mortgages: the forms offer a snapshot of a person's financial position and their financial decision making processes," the Foundation wrote in July.