The Library of Congress (L.C.) Classification System 

This guide is designed to briefly introduce you to the Library of Congress classification system. This system is used both at Skillman and Kirby Libraries. Skillman Library also uses the Dewey Decimal classification system which will be discussed separately. The following is a series of brief discussions on different aspects of this system so let's begin!

• The Library of Congress (or "L.C." for short) classification system uses alphanumerics to categorize and organize library materials. Without this kind of system, it would practically be impossible to keep track of the library's expansive collection. 

• A  collection may contain materials in various format: books, pamphlets, periodicals (such as magazines, journals), maps, DVDs, etc. — each material is assigned a unique alphanumeric code called a “call number.” 

• Think of a "call number" as a unique address much like the address to your house — no two are exactly alike (unless they are the exact copies, in which case, we will distinguish them by adding "copy 1"; "copy 2" and so on).

A call number is typically broken down into four to five segments (sometimes more):

Segment 1 typically contains one, two  or sometimes three letters (e.g. “BD”; "KHR")

Segment 2 can be a whole or decimated number (e.g. “444” or decimated, “54.5”)

Segment 3 will have a decimal point followed by an alphanumeric combination  (e.g. “.S68”, ".G2423", etc).  

Segment 4 typically has the year of publication, but it can sometimes be another alphanumeric line, or a volume number, a series number, a copy number, etc. Below are examples on what they typically look like: 

In our examples above, we have a call number presented in a stacked format (left) and then in one line (right).  For demonstration purposes, we'll call the example on the left, "portrait" and the one to the right, "landscape" orientation. When you begin handling library materials, you'll find these two types of orientation throughout the collection. 

Call numbers are organized and ordered by comparing letters to letters (and numbers to numbers). Let's look at alphabetizing words:

"aloe"  goes before "berry" goes before "bone" goes before "draw"

By looking at this list, we can see a few basic principles:

1.  words are ordered based on first letter (aloe  comes before  berry) because "a"   comes before  "b"

2  if the first letters are the same, the next non-similar letter are then compared: "berry"  comes before "blend" and if there is no other letters (or numbers) to compare, then "bone"  comes before "boneless".)

Let's now try this principle when we have alphanumberic combinations. Begin by comparing the 1st segment which usually begins with letters in the Library of Congress system:

• An item with  the call number E 842.9 .H3  will come before HC 57 .K4 1920,

  • • • • Why? Because E 842.9 .H3  come before HC 57 .K4 1920 alphabetically. Let's try another example:

• BD 444 .S42  will come before BF 371 .S4756 T3 1982

Practice Quiz #1

Which pair of call numbers are ordered correctly?

If two call numbers have the same first segments, continue on to the 2nd segment. Remember, the 2nd segment is typically a number. Hence,

• D 228 .T46  comes before D 727 .C7 

• D 6 .H99 1934  comes before D 56 .R45 2019 

and if the number is decimated:

• HB 139 .R37  comes before HB 139.5 .B25

Ready for Practice Quiz #2?

Which pair below is ordered correctly if you were to compare the second segments?

If both segments 1 and 2  are exactly the same, the next step is to then compare what is in segment 3 which typically starts with a decimal point followed by an alphanumberic combination. When comparing alphanumeric combinations, they are compared on a "digit-by-digit" basis. Letters are compared first, followed by numbers:

JD 341 .F41 2003  comes before JD 341 .G3 2001
KF 9923 .K90 2024  comes before KF 9923 .Q2 2001

Question: What should be done if the letters are the same? 

Answer: Continue to the next digit...

JD 341 .F56 1989  comes before JD 341 .F6 2022 

Question: In the example above, why did the segment “.F56”  comes before “.F6”? Doesn’t “6” come before “56”? 

Answer: Remember, the rule states to compare the 3rd segment on a "digit-by-digit" basis, not as whole numbers.

Question: What happens if the 1st, 2nd and 3rd segments of two call numbers are all the same? 

Answer: Simply continue to the next segment until there's a break in the pattern.  

Examples:

• ND 547 .R4 K43  comes before ND 547 .R4 P6

• L200 .N345 2012  comes before L200 .N345 2016 

• Z9 .H45 1988 copy 1  comes before Z9 .H45 1988 copy 2

• C3561 .D1 1942 vol. 1  comes before C3561 .D1 1942 vol.  2

The 4th segment typically contains information like the year (of publication), volume number and/or copy number. Sometimes, it may include all of these designations prompting additional segments than the typical four. 

Years are organized chronologically (from oldest to newest), volumes ("v. " or "vol.  ") and copy ("c. " or "cop." or "copy") numbers are sorted in ascending order. 

More Examples:

• F 20 .P390 1932  comes before F 20 .P390 1934 

• ND 547.5 .I4 1968 v.1  comes before ND 547.5 .I4 1968 v.2

• DS2910 .A234 2012 c.1  comes before DS2910 .A234 2012 c.2 (sometimes abbreviated as "c." or "cop.")

• AN2 .K44 2011 v.1  comes before AN2 .K44 2011 v.2         (sometimes abbreviated as "vol.")

Are you beginning to see the overall pattern? 

• • Compare, determine which comes first...

  • If the information is the same, continue comparing until there is a break in the pattern

Question: What if there is "no-thing" or digits to compare?
Answer: If there is "no-thing" to compare to, it shall then go first. 

Example:

• HB 1 .H35 1964 comes before HB 1 .H35x 1964

A good mnemonic device is the phrase: “No-thing comes before something.” If there are no more digits, then that call number will be first or before the other call number. In the example above, we have two call numbers that are alike with the exception of the "x" in the second call number. Since the first call number no longer has a digit to compare the "x" to, it will precede the call number that has more digit(s). This is also applied to segments. 

PRACTICE QUIZ #3

Which pair below is ordered correctly?

Here's another scenario you may encounter:

GR 360 .S4 K3g comes before GR 360 .S4 K32

What happened here? What's the pattern?

The example demonstrates another rule---when comparing digits: letters comes before numbers, hence: K3g comes before K32.

Periodicals

When dealing with bound periodicals (magazines, journals, newspaper) additional segments may be encountered: number (sometimes abbreviated as “no.”); part (sometimes abbreviated as “pt.”)---these should be ordered in an ascending order: “part 1” or “pt. 1” before “part 3” or “pt. 3”; “no. 7” before “no. 9”; "part A" before "part B", etc. 

Here are examples of how the call numbers may appear:

Updated: 18 December 2025