The Chimney Safety Institute of America is the premier chimney safety program in the United States.  The CSIA website provides information regarding what is required for CSIA certification:

CSIA Certified Chimney Sweeps keep abreast of the current developments and the technology of their trade. They are knowledgeable about the most recent National Fire Protection Association standards as well as the specifics of state and local codes covering their geographic area. In order to ensure a verifiable level of expertise within the trade, the Chimney Safety Institute of America administers the CSIA Certified Chimney Sweep Program.  

It is an educational and testing program designed to assess a chimney sweep's knowledge of:

(1) technical issues related to chimney construction and dynamics

(2) solid fuel appliances and EPA requirements

(3) the physics of wood burning and creosote formation

(4) codes, clearances and standards

(5) the practices and techniques of the trade.

Throughout most of the 50 states, the homeowner's best gauge of a chimney serviceperson's knowledge is the CSIA Certified Chimney Sweep credential. C.S.I.A. Certified Sweeps are tested every three years, and display a dated, photo-ID badge. A good way to be sure the sweep servicing your chimney is currently Certified is to check the search engine on the CSIA website or call the CSIA office. These sweeps must also sign a CSIA Chimney Sweep Code of Ethics to help insure homeowners get not only a knowledgeable sweep, but an honest one. Don't settle for less!"