21st Century Investment Act of 2012 - Amends the Internal Revenue Code to: (1) make permanent the tax credit for increasing research activities, (2) increase such credit for amounts paid or incurred for research substantially all of which occurs in the United States, (3) increase the rate of the simplified research tax credit, and (4) increase through December 31, 2020, the domestic production activities tax deduction for income attributable to the manufacture or production of property with respect to which substantially all of the research and development occurred in the United States.