Directories are often a good first stop. Indeed, they are essential when researching private and small, local companies because this type of source may be one of the few places a business shows up in published sources.
You can “chase” the company around to various locations, sometimes find other locations (showrooms, manufacturing, etc), and in some cases you can find the names/positions of the executives and a few other pieces of information. They can also be helpful for estimating how long a business was active by seeing when they were first listed (rough approximation of start time) and when they ceased to be listed (rough approximation of when the company “died”).
There are different types of directories and related sources. Some focus on a particular geographic area while others focus on particular industries. They all have their limitations and strengths.
You will need the older items. It may be harder to find some types of directories particularly if you are looking for older items and a large collection of older items.
These types of directories are likely to be much more widely available. Since many local libraries and historical societies have kept them for local history and genealogical reasons, it might be good to look to these institutions.
While many libraries may have telephone books and yellow pages in special collections, there may be other directories within a library's collections. If you are looking for directories in online catalogs using Library of Congress Subject Headings you may want to try using subject headings. These particular subject headings are for more general directories geared for specific locations.
Since yellow pages and telephone books were widely distributed to those with telephones, collections of them will likely be more widely available in state/local public libraries and historical societies. The Library has many of them from around the country as an uncataloged collections and, it is likely this is how they are found in other institutions as well. Also, it is likely that you will need know how the title is organized in terms of what places are covered by a particular phonebook to use them effectively. Often coverage is by city/town, but it can be by county, groups of cities, or regional—a local library or historical society will likely be able to assist with understanding coverage.
City business directories were published by private publishers and functioned in much the same way as yellow pages and residential telephone books. While some were still published later in the 20th and into the 21st century depending on the publisher, most of these are good for those needing directories from the years before the rise of telephone books. Like with telephone books and specifically yellow pages, these are often organized by city usually, but there are some cases when the organization is regional or by county. Again, look to a local library or historical collection either for the print version or look at ancestry.com which has some of these types of directories Sometimes show up digitized in HathiTrust and Internet Archive, but public libraries digitize as well. For example, New York Public digitized the Trow's directory External and Boston Public Library External and the San Francisco Public Library External did the same with their city's directories. It is not uncommon for libraries and interested historians or genealogists to create a web page collecting links and notes about where directories for that place can be found that may help speed up you finding the one you need — here is a good example for Chicago External.
The Library has many of these directories in print and in microform. The print volumes are mostly uncataloged and requesting them is best done in person in the Science & Business Reading Room on the 5th floor of the Adams Building. The microfilm versions are self-serve in the Microform Reader Center across from the entrance to the Main Reading Room in the Thomas Jefferson Building but there is an inventory of the holdings for this collection linked to below.
There are a few things to keep in mind for these geographic based directories that may make finding them easier:
These directories do show up in a few databases, most notably Ancestry.com. However, using them is challenging because these directories were included for genealogical purposes and not for researching companies. If you have an owner's name, you can search on that person and results will include directories. You can also limit searching to just the directories. The Quick Links will take you to City Directories and then you can either search or drill down to a particular place/year through the state to the city/county under the Featured data collections. Below are a few search tips:
These "reverse directories" are sometimes referred to as criss-cross or street address directories and are often organized by address but can only really helpful if you have a location (and for some phone number). They can be good for understanding a neighborhood and can be good for environmental remediation situations.
These sets may have been leased, and finding them may be a bit more challenging. The Library likely has the single best collection of locations and years, but some local libraries/historical societies may have copies for places that are important to them. The inventories that we do have are linked to below but not all places are covered and holdings are not necessarily complete.
If you need to search the catalog the below searches and suggestions should get you started.
Below are databases and open access resources and inventories developed for some of the Library's collection mentioned above. The subscription resources marked with a padlock 
are available to researchers on-site at the Library of Congress. If you are unable to visit the Library, you may be able to access these resources through your local public or academic library.
There are many industry specific sources that are good for research. Some are pure directories some are directory -adjacent. These types of sources can often include pieces of information specific to that industry that a more general geographic focused directory wouldn't include. Many of today's directories do have their roots in print sources. It is the older editions, if they are available, that can be very useful to researchers.
The Ward's Business Directory of U.S. Private and Public companies is a large directory set that began in the late 1980s and while not strictly industry specific, it does have volumes that group businesses by industry. It was a standard reference title in many libraries. While some institutions may not have retained older editions it is a title to look for.
If the business is a big or part of an industry with a lot of published materials like manufacturing or finance/banking, you may want to see what is available that is specific to that industry. Some sources will be more typical in nature with names, addresses, and other similar type of information like Polk's Bank Directory, Thomas Register, and titles from Davison Pub. Co. or AM Best for insurance (Best's Insurance Reports: Property / Casualty and Best's Insurance Reports: Life / Health ). Other sources are similar to traditional directories and includes sources like credit reference books. These types of titles were used by business to determine providers of particular products, but also if they were someone good to do business with. They often include information or code systems for revenue, bill paying ability, and other types of information. These directories are generally organized by location (state and city/town) so you will need to know a location. Examples of these types of things are: United Beverage Bureau Book, Lumberman’s Red book, Lyon Red Book ( Furniture Trade and Kindred Branches), and Apparel Trade Book.
There are many publishers publishing any number of industry specific directories or similar sources, and we can't include them all here. To find industry directories you can use Subject Headings to find more. Of course if you don't know an industry subject heading, try a Keyword or Keyword in the Subject Heading search in the Library catalog using the industry and also the word "directories."
Dun & Bradstreet (also known as Duns, D&B, the Mercantile Agency, etc.) has been publishing many different titles since the mid-19th century . It was, and is, a credit rating agency and the information in the various titles reflects that. All titles cannot be included here but if you are looking for other publications there is an inventory/listing on the business homepage.
The longest running one often referred to as the Reference Book of American Business (or variations of that) it is a directory, but it is not one that includes addresses, telephone numbers, and the like. It lists companies by state, and then by county/city and has a code system for different pieces of information - industry, bill paying ability, and revenue range. It came out 5 times a year and was leased in many cases, so it is likely that only random volumes are available. However, the Library has a mostly complete set. Below is a webinar hosted in August 2022 that looks at the set and offers some tips and tricks for using the set.
There is a sister source, the Million Dollar Directory which started in 1957 as a directory of companies – public and private – with sales over a million dollars. However, over time some parameters were changed and eventually most people accessed the title as an online database (though there were print editions).The Library does have this in print as well as part of the Mergent Archives database.
They also produced a number of Regional Business directories but those don't appear until much later so they won't be helpful for many older companies. These titles will come up using subject heading, but you wills see them searching the title D & B regional business directory.
Dun & Bradstreet Reference Book of American Business
Dun & Bradstreet Reference Book CollectionOn August 2, 2022, the staff of Business Reference Services hosted a webinar covering the newly digitized collection of Dun & Bradstreet Reference Book of American Business for the years 1900-1924. It was an introduction to the information in the title, as well as providing a brief introduction in how it was organized and how best to use it.
If you are looking for the text transcript one is available.
