| Name | Phone | Category |
| Rager, Lehman & Houck, P.C. | (301) 696-9449 | Accountants/CPA's |
| Ramar Moving Systems, Inc. | (301) 694-3366 | Moving/Storage |
| Ramar Record Retention | (301) 695-6312 | Record Retention & Retrieval |
| Raymond Raedy | (919) 967-8816 | Consultants |
| RE/MAX 100 - West | (301) 788-5688 | Real Estate Companies |
| Real Estate Teams LLC-Ahearn | (301) 695-3020 | Real Estate Companies |
| Real Estate Teams, LLC | (301) 695-3020 | Real Estate Companies |
| Recomm Inc. | 301-829-1281 | Telecommunications |
| Red Wing Shoe Store (MJ&S, Inc.) | (301) 815-5430 | Retailers |
| Mr. Earl James Reinsch | 301-696-0657 | Individuals |
| Reliable Recycling Center | (301) 663-4482 | Recycling Companies |
| Adrian McC. Remsberg | 301-371-6355 | Individuals |
| Renaissance Chef Catering Company | (301) 228-2433 | Caterers |
| Rentals Unlimited Inc. | (301) 663-9200 | Equipment Rental |
| Residence Inn Frederick By Marriott | (301) 360-0010 | Lodging/Hotels & Motels |
| Horning Brothers | (301) 662-3303 | Apartments |
| Resthaven Memorial Gardens, Inc. | (301) 898-7177 | Funerals/Cemeteries |
| Rib City/ESB Foods Inc. | 301-325-8225 | Restaurants/Cafes |
| Rico Service Corporation | (301) 358-2657 | Computers/Internet |
| RidgeRunner Publishing | (301) 620-9595 | Publishers/Publications |
| Rightway Plumbing | 717-762-5988 | Plumbing Services/Supplies |
| River & Trail Outfitters | (301) 695-5177 | Outdoor Recreation |
| Rodgers Consulting | (301) 253-6609 | Engineering Services |
| Rogers Engraving & Stamps + Plus, LLC | (301) 663-4311 | Awards, engraving, recognition products |
| Romano's Macaroni Grill | (301) 624-1026 | Restaurants/Cafes |
| Routzahn's Furniture | (301) 662-2141 | Retailers |
| Roy Jorgensen Associates Inc. | (301) 831-1000 | Facility Maintenance Management |
| RSM McGladrey, Inc. | (301) 712-9600 | Accountants/CPA's |
| Ruppert Landscape | 301-620-7551 | Lawn/Garden/Landscaping Care |
| Ruppert Properties | (301) 482-0300 | Real Estate Companies |
| RWS Consulting Corp | (202) 409-8113 | Advertising |
| Ryan & Wetmore, PC | (301) 668-7860 | Accountants/CPA's |