ative ▁branch ▁ ▁government ▁ag ency ▁that ▁provides ▁aud iting , ▁evaluation , ▁and ▁investig ative ▁services ▁for ▁the ▁United ▁States ▁Congress . ▁It ▁is ▁the ▁supre me ▁aud it ▁institution ▁of ▁the ▁federal ▁government ▁of ▁the ▁United ▁States . ▁It ▁ident ifies ▁its ▁core ▁" mission ▁values " ▁as : ▁account ability , ▁integrity , ▁and ▁reli ability . ▁It ▁is ▁also ▁known ▁as ▁the ▁" con gression al ▁watch dog ". ▁ ▁Pow ers ▁of ▁G A O ▁Work ▁of ▁G A O ▁is ▁done ▁at ▁the ▁request ▁of ▁con gression al ▁comm itte es ▁or ▁sub comm itte es ▁or ▁is ▁mand ated ▁by ▁public ▁laws ▁or ▁committee ▁reports . ▁It ▁also ▁undert akes ▁research ▁under ▁the ▁authority ▁of ▁the ▁Com pt roller ▁General . ▁It ▁supports ▁con gression al ▁o vers ight ▁by : ▁ ▁aud iting ▁ag ency ▁operations ▁to ▁determine ▁whether ▁federal ▁funds ▁are ▁being ▁spent ▁efficiently ▁and ▁effectively ; ▁ ▁investig ating ▁alleg ations ▁of ▁illegal ▁and ▁impro per ▁activities ; ▁ ▁reporting ▁on ▁how ▁well ▁government ▁programs ▁and ▁policies ▁are ▁meeting ▁their ▁object ives ; ▁ ▁performing ▁policy ▁anal ys es ▁and ▁out lin ing ▁options ▁for ▁con gression al ▁consideration ; ▁ ▁issu ing ▁legal ▁dec isions ▁and ▁opinions ; ▁ ▁advis ing ▁Congress ▁and ▁the ▁heads ▁of ▁executive ▁ag encies ▁about ▁ways ▁to ▁make ▁government ▁more ▁efficient ▁and ▁effective . ▁ ▁Product s ▁of ▁G A O ▁ ▁Product s ▁of ▁G A O ▁include ▁the ▁following : ▁ ▁reports ▁and ▁written ▁correspond