- Accountants
- Accounting Service
- Accounting Software
- Acoustic Consultants
- Acoustical Contractors
- Actuaries
- Acupuncturists
- Adaptive Clothing
- Addiction Treatments
- Adjusters
- Adoption Service
- Adult Entertainment
- Adventure Games
- Advertising Agencies
- African Restaurants
- Agricultural Consultants
- Aids Services
- Air Cargo Service
- Air Conditioner Repair
- Air Conditioning
- Air Conditioning Contractors
- Air Pollution Controls
- Air Quality Service
- Air Travel
- Aircraft Charters
- Aircraft Dealers
- Aircraft Engines
- Aircraft Maintenance
- Airports
- All-Terrain Vehicles
- Alterations
- Alternative Health
- Alternative Therapies
- Alternators
- Aluminum
- Aluminum Fabricators
- American Restaurants
- Amusement Machines
- Amusement Places
- Animal Breeders
- Animal Control
- Animal Medications
- Animal Shelters
- Annuities
- Answering Machines
- Antique Dealers
- Antiques
- Apartment Hotels
- Apartment Rental
- Apartments
- Appliance Parts
- Appliance Repair
- Appliance Wholesalers
- Appraisers
- Arbitration Service
- Architects
- Architectural Drawing
- Architectural Technologists
- Archives
- Arenas
- Armoured Cars
- Aromatherapy
- Art Galleries
- Art Metal Works
- Art Schools
- Art Supplies
- Artificial Limbs
- Artists
- Arts and Crafts Classes
- Arts and Crafts Stores
- Arts and Crafts Supplies
- Asbestos Removal
- Asbestos Testing
- Asian Noodle Restaurants
- Asian Restaurants
- Assembly Service
- Assisted Living
- Association Management
- Associations
- Auctions
- Audiologists
- Audiovisual Consultants
- Audiovisual Equipment
- Audiovisual Production Service
- Auto Body Repair and Painting Shops
- Auto Body Shop Equipment
- Auto Glass
- Auto Part Manufacturers
- Auto Repair Equipment
- Auto Repair Garages
- Auto Repair Self-Service Garages
- Automatic Fire Sprinkler Systems
- Automation Systems
- Aviation Consultants
- Awnings