| 9241 | Athletic clubs, physical fitness facilities | |
| 4520 | Athletic field construction, general contractors | |
| 5232 | Athletic footwear, retail | |
| 5131 | Athletic footwear, wholesale | |
| 5239 | Athletic goods, retail | |
| 5232 | Athletic shoe stores, retail | |
| 1920 | Athletic shoes, manufacturing | |
| 9214 | Athletic skill level evaluator, independent | |
| 1730 | Athletic socks, knitting | |
| 1810 | Athletic team uniforms, men's and boys', cut and sewn from material owned by others | |
| 1810 | Athletic team uniforms, women's, misses' and girls', cut and sewn from materials owned by others | |
| 1810 | Athletic uniforms, cut and sewn from purchased fabric | |
| 1810 | Athletic uniforms, men's and boys', cut and sewn from purchased fabric | |
| 1810 | Athletic uniforms, women's, misses' and girls', cut and sewn from purchased fabric | |
| 0500 | Atlantic saltwater fishing | |
| 2221 | Atlases, printing without publishing | |
| 2211 | Atlases, publishers | |
| 2211 | Atlases, publishing | |
| 2211 | Atlases, publishing and printing combined | |
| 5139 | Atlases, wholesale | |
| 6719 | ATM network providers | |
| 3000 | ATM's (automatic teller machines), manufacturing | |
| 7513 | Atomic Energy Commission (except inspection and defense) | |
| 7513 | Atomic energy inspection and regulation offices | |
| 3699 | Atomizers (e.g., perfume), manufacturing | |
| 3311 | Atomizers, medical, manufacturing | |
| 2423 | Atropine and derivatives (i.e., basic chemicals), manufacturing | |
| 1912 | Attaché cases, all materials, manufacturing | |
| 5232 | Attaché cases, retail | |
| 3120 | Attachment plugs, caps, taps and connectors, manufacturing | |
| 2921 | Attachments for powered lawn and garden equipment, manufacturing | |
| 2930 | Attic fans, manufacturing | |
| 4530 | Attic space insulating | |
| 7523 | Attorney generals' offices, federal government | |
| 7523 | Attorney generals' offices, state | |
| 7523 | Attorneys general's offices | |
| 7411 | Attorneys, private practice | |
| 7499 | Auctioneering service, on a commission or fee basis, not done on own facilities (except currency and tobacco) | |
| 5219 | Auctioneering, with own facilities, open to the general public | |
| 5010 | Auctioneers, automobile, with own facilities, not open to the general public | |