A tax credit is a direct, dollar for dollar, reduction in the amount of money a taxpayer must pay in taxes for a given year. For example, if a taxpayer owest $6,000 in taxes to the IRS, but has a $3000 credit, he or she only pays $3000. A tax credit is much better than a decudtion which merely reduces a taxpayer's income and puts him or her in a lower tax bracket.
The Louisiana Office of Cultural Development Division of Historic Preservation is responsible for processing Historic Tax Credits in Louisiana. The initial paper is somewhat detailed, but once you get past the intial application it's mostly downhill. I find the initial work is well worth the money saved. Homeowner's may qualify for a 25% tax credit(50% for vacant and blighted properties) against their individual state income taxes when they rehabilitate their historic home. The property must be the owner's primary residence, however there is a separate program for income producing property.
Here is a quick overview of the Tax Incentive programs available in Louisiana.Tax Incentive Programs - LA_Tax_Incentives_Program_Quick_Reference_Guide.pdf
For more information check out the States site at http://www.crt.state.la.us/hp/tax_incentives_program.aspx