Your federal income tax pays your share of the cost of running the federal government and the cost of the services it provides, including the military, roads, bridges, education and much more.  The Internal Revenue Service (IRS) is the federal agency responsible for collecting income tax.  With the support of federal laws requiring employers and banks to report your salary and other earnings, the IRS is very effective in collecting taxes, imposing fines and interest and criminally prosecuting people who don’t pay the entire tax they owe.