I think you understand what 179 bonus depreciation "is", my comments were directed to the poster above you and his worn out, boring, and demonstratively wrong supply side argument that cutting taxes increases government revenue. Make no mistake, Sec 179 extension is a tax cut - an expensive one, costing the Treasury some $27 Billion per year. Sec. 179, as a permanent feature of the tax code, loses what little stimulative effect it might have.  What is the incentive to accelerate capital purchases if you are going to get the same deal next year?  Add to that Capital investments are already given preferential tax treatment, 179 is just "piling on." And finally, bonus depreciation schemes also narrow the tax base and make it more difficult to achieve real tax reform.