In the Latin script, majuscules ( or ) are A, B, C, etc.; minuscules are a, b, c, etc.

Most occidental (Western) languages (certainly those based on the Latin, Cyrillic, Greek, Armenian alphabets, and Coptic alphabets) use multiple letter-cases in their written form as an aid to clarity. Scripts using two separate cases are also called "bicameral scripts". Many other writing systems (such as those used in the Georgian language, Glagolitic, Arabic, Hebrew, and Devanagari) make no distinction between capital and lowercase letters – a system called unicase. If an alphabet has case, all or nearly all letters have both forms. Both forms in each pair are considered to be the same letter: they have the same name, same pronunciation, and will be treated identically when sorting in alphabetical order. An example of a letter without both forms is the German ß (ess-tsett), which exists only in minuscule. When capitalized it normally becomes two letters ("SS"), but the ß letter may be used as a capital to prevent confusion in special cases, such as names. This is because ß was originally a ligature of the two letters "ſs" (a long s and an s), both of which become "S" when capitalized. It later evolved into a letter in its own right. (ß is also occasionally referred to as a ligature of "sz", which recalls the way this consonant was pronounced in some medieval German dialects. The original spelling sz is preserved in Hungarian and pronounced [s].)

Languages have capitalization rules to determine whether majuscules or minuscules are to be used in a given context. In English, capital letters are used as the first letter of a sentence, a proper noun, or a proper adjective, and for initials or abbreviations. The first-person pronoun "I" and the interjection "O" are also capitalized. Lower-case letters are normally used for all other purposes. There are however situations where further capitalization may be used to give added emphasis, for example in headings and titles or to pick out certain words (often using small capitals). There are also a few pairs of words of different meanings whose only difference is capitalization of the first letter. Other languages vary in their use of capitals. For example, in German the first letter of all nouns is capitalized, while in Romance languages the names of days of the week, months of the year, and adjectives of nationality, religion and so on generally begin with a lower-case letter.

European languages, except for Ancient Greek and Latin, did not make the case distinction before about 1300. In Latin, papyri from Herculaneum dating before 79 have been found which include lower-case letters a, b, d, h, p, and r. According to papyrologist Knut Kleve, "The theory, then, that the lower-case letters have been developed from the fifth century uncials and the ninth century Carolingian miniscules seems to be wrong."

Both "majuscule" and "minuscule" letters existed, but the printing press had not yet been invented, and a given handwritten document could use either one size/style or the other. However, before about 1700 literacy was very low in Europe and the Americas, hence even handwriting was not used or understood by more than about 1% of people. Therefore, there was not any motivation to use both upper case and lower case letters in the same document as all documents were used by only a small number of scholars.

The timeline of writing in Western Europe can be divided into four eras:

• Greek majuscule (9th–3rd century B.C.) in contrast to the Greek uncial script (3rd century BC – 12 century AD) and the later Greek minuscule
• Roman majuscule (7th century BC – 4th century AD) in contrast to the Roman uncial (4th–8th century BC), Roman Half Uncial, and minuscule
• Carolingian majuscule (4th–8th century AD) in contrast to the Carolingian minuscule (around 780 – 12th century)
• Gothic majuscule (13th and 14th century), in contrast to the early Gothic (end of 11th to 13th century), Gothic (14th century), and late Gothic (16th century) minuscules.

Traditionally, certain letters were rendered differently according to a set of rules. In particular, those letters that began sentences or nouns were made larger and often written in a distinct script. There was no fixed capitalization system until the early 18th century. The English language eventually dropped the rule for nouns, while the German language kept it.

Similar developments have taken place in other alphabets. The lower-case script for the Greek alphabet has its origins in the 7th century and acquired its quadrilinear form in the 8th century. Over time, uncial letter forms were increasingly mixed into the script. The earliest dated Greek lower-case text is the Uspenski Gospels (MS 461) in the year 835. The modern practice of capitalizing the first letter of every sentence seems to be imported (and is rarely used when printing Ancient Greek materials even today).

The Samaritan alphabet also had lower-case letters, making it relatively unusual among abjads such as Hebrew, Syriac and Arabic, which tend to be written without case.

Various patterns of cases are available, often with the compartments for lower-case letters varying in size according to the frequency of use of letters, so that the commonest letters are grouped together in larger boxes at the centre of the case. The compositor takes the letter blocks from the compartments and places them in a composing stick, working from left to right and placing the letters upside down with the nick to the top, then sets the assembled type in a galley.

The Oxford Universal Dictionary on Historical Advanced Proportional Principles (reprinted 1952) indicates that this usage of "case" (as the box or frame used by a compositor in the printing trade) was first used in 1588. Originally one large case was used for each typeface, then "divided cases", pairs of cases for upper and lower case, were introduced in the region of today's Belgium by 1563, England by 1588, and France before 1723. Though pairs of cases were used in English-speaking countries and many European countries, in Germany and Scandinavia the single case continued in use.

For paleographers, a majuscule script is any script in which the letters have very few or very short ascenders and descenders, or none at all (for example, the majuscule scripts used in the Codex Vaticanus Graecus 1209, or the Book of Kells).

The word minuscule is often spelled miniscule, by association with the unrelated word miniature and the prefix mini-. This has traditionally been regarded as a spelling mistake (since minuscule is derived from the word minus), but is now so common that some dictionaries tend to accept it as a nonstandard or variant spelling. However, miniscule is still less likely to be used for lower-case letters.

Also similar to case is recent usage in Georgian, where some authors use isolated letters from the Asomtavruli alphabet within a text otherwise written in Mkhedruli in a fashion that is reminiscent of modern usage of letter case in the Latin, Greek, and Cyrillic alphabets.

In scripts with a case distinction, lower case is generally used for the majority of text; capitals are used for capitalization, acronyms, medial capitals, and emphasis (in some languages).

 Capitalization is the writing of a word with its first letter in uppercase and the remaining letters in lowercase. Capitalization rules vary by language (e.g. capitalization in English) and are often quite complex, but in most modern languages that have capitalization, the first word of every sentence is capitalized, as are all proper nouns. Some languages, such as German, capitalize the first letter of all nouns; this was previously common in English as well. (See the article on capitalization for a detailed list of norms).

In English, a variety of case styles are used in various circumstances:

• Capitalization in English, in terms of the general orthographic rules independent of context (e.g., title vs heading vs text), is universally standardized for formal writing. For example, it is universal to begin a sentence with a cap, and to cap proper nouns, wherever formal orthography is in force. (Informal communication, such as texting, IM, or a handwritten sticky note, may not bother, of course; but that's because its users usually do not expect it to be formal.)
  • Sentence case: The most common in English prose. Generally equivalent to the baseline universal standard of formal English orthography mentioned above; that is, only the first word is capitalized, except for proper nouns and other words which are generally capitalized by a more specific rule.
  • Title Case: All words are capitalized except for certain subsets defined by rules that are not universally standardized. The standardization is only at the level of house styles and individual style manuals. (See further explanation below at Headings and publication titles.)
  • ALL CAPS: Only capital letters are used. Capital letters were sometimes used for typographical emphasis in text made on a typewriter. However, long spans of Latin-alphabet text in all upper-case are harder to read because of the absence of the ascenders and descenders found in lower-case letters, which can aid recognition. With the advent of the Internet, all-caps is more often used for emphasis; however, it is considered poor "netiquette" by some to type in all capitals, and said to be tantamount to shouting.
  • : Capital letters are used which are the size of the lower-case "x". Slightly larger small caps can be used in a fashion. Used for initialisms, names, mathematical entities, computer commands in printed text, business or personal printed stationery letterheads, and other situations where a given phrase needs to be distinguished from the main text.
  • lowercase only: Sometimes used for artistic effect, such as in poetry. Also commonly seen in computer commands and SMS language, to avoid pressing the shift key in order to type quickly.

In some traditional forms of poetry, capitalization has been conventionally used as a marker to indicate the beginning of a line of verse independent of any other grammatical feature.

As for whether hyphenated words are capitalized not only at the beginning but also after the hyphen, there is no universal standard; variation occurs in the wild and among house styles (e.g., The Letter-Case Rule in My Book; Short-term Follow-up Care for Burns). Traditional copyediting makes a distinction between "temporary compounds" (such as many nonce [novel instance] compound modifiers), in which every word is capped (e.g., How This Particular Author Chose To Style His Autumn-Apple-Picking Heading), and "permanent compounds", which are terms that, although compound and hyphenated, are so well established that dictionaries enter them as headwords (e.g., Short-term Follow-up Care for Burns).

The convention followed by many British publishers (including scientific publishers, like Nature, magazines, like The Economist and New Scientist, and newspapers, like The Guardian and The Times) is to use sentence-style capitalization in titles and headlines, where capitalization follows the same rules that apply for sentences. This convention is sometimes called sentence case. It is also widely used in the United States, especially in newspaper publishing, bibliographic references and library catalogues. Examples of global publishers whose English-language house styles prescribe sentence-case titles and headings include the International Organization for Standardization.

In creative typography, such as music record covers and other artistic material, all styles are commonly encountered, including all-lowercase letters and mixed case (StudlyCaps).

Several information technology products are titled in CamelCase, deriving from a computer programming practice.

One British style guide mentions a form of title case: R.M. Ritter's "Oxford Manual of Style" (2002) suggests capitalizing "the first word and all nouns, pronouns, adjectives, verbs and adverbs, but generally not articles, conjunctions and short prepositions".

• CamelCase: First letter of each word is capitalized, spaces and punctuation removed. If the very first letter is capitalized, as in "CamelCase" (or "PowerPoint"), the term "upper camel case" may be used; this is also known as "Pascal case" or "Bumpy case". "Lower camel case" describes a variation, as in "camelCase" (or "iPod" or "eBay"), in which the very first letter is in lower case.
• Start case: First letter of each word capitalized, spaces separate words. All words including short articles and prepositions start with a capital letter. For example: "This Is A Start Case".
• Snake case: punctuation is removed and spaces are replaced by single underscores. Normally the letters share the same case (either UPPER_CASE_EMBEDDED_UNDERSCORE or lower_case_embedded_underscore) but the case can be mixed.
• Studly caps: Mixed case, as in "StUdLyCaPs", with no semantic or syntactic significance to the use of the capitals. Sometimes only vowels are upper-case, at other times upper and lower case are alternated, but often it is just random. The name comes from the sarcastic or ironic implication that it was used in an attempt by the writer to convey their own coolness. (It is also used to mock the violation of standard English case conventions by marketers in the naming of computer software packages, even when there is no technical requirement to do so—e.g., Sun Microsystems' naming of a windowing system NeWS.)

 C and C++, as well as any C-like language that conforms to its standard library, provide these functions in the file ctype.h:
<source lang="c"> char upperA = toupper('a'); char lowerA = tolower('A'); </source>

Case folding is different with different character sets. In ASCII or EBCDIC, case can be folded in the following way, in C:
#define toupper(c) (islower(c) ? (c) - 'a' + 'A' : (c)) #define tolower(c) (isupper(c) ? (c) - 'A' + 'a' : (c))

This only works because the letters of upper and lower cases are spaced out equally. In ASCII they are consecutive, whereas with EBCDIC they are not; nonetheless the upper case letters are arranged in the same pattern and with the same gaps as are the lower case letters, so the technique still works.

Some computer programming languages offer facilities for converting text to a form in which all words are first-letter capitalized.  Visual Basic calls this "proper case"; Python calls it "title case". This differs from usual title casing conventions, such as the English convention in which minor words are not capitalized.

As briefly discussed in Unicode Technical Note #26, "In terms of implementation issues, any attempt at a unification of Latin, Greek, and Cyrillic would wreak havoc [and] make casing operations an unholy mess, in effect making all casing operations context sensitive [...]". In other words, while the shapes of letters like A, B, E, H, K, M, O, P, T, X, Y and so on are shared between the Latin, Greek, and Cyrillic alphabets (and small differences in their canonical forms may be considered to be of a merely typographical nature), it would still be problematic for a multilingual character set or a font to provide only a single codepoint for, say, uppercase letter B, as this would make it quite difficult for a wordprocessor to change that single uppercase letter to one of the three different choices for the lower case letter, b (Latin), β (Greek), or в (Cyrillic). Without letter case, a 'unified European alphabet'—such as ABБCГDΔΕZЄЗFΦGHIИJ...Z, with an appropriate subset for each language—is feasible; but considering letter case, it becomes very clear that these alphabets are rather distinct sets of symbols.

• The German letter ß exists only in lowercase (but see Capital ß), and is capitalized as "SS".
• The Greek letter Σ has two different lowercase forms: "ς" in word-final position and "σ" elsewhere.
• The Cyrillic letter Ӏ usually has only a capital form, which is also used in lowercase text.
• Unlike most Latin-script languages that use uppercase "I" and lowercase "i", Turkish has dotted and dotless I independent of case.

• Font effects such as italic type or oblique type, boldface, and choice of serif vs. sans-serif
• Typographical conventions in mathematical formulae include the use of Greek letters and the use of Latin letters with formatting such as blackboard bold and blackletter
• Choice of character set, for example switching between kanji, hiragana, katakana, and rōmaji in the Japanese writing system.

• All caps
• CamelCase
• Capitalization
• Case folding
• Roman cursive
• Roman square capitals
• Sentence case
• Shift key
• Small caps
• StudlyCaps
• Text figures for upper/lowercase numerals
• Unicase

• SongCase.com, Online tool]for capitalizing song titles
• Change Text Case Upper to Lower and Lower to Upper case]* Convert text to title case]*Printing capitals worksheet]*Codex Vaticanus B/03]Detailed description of Codex Vaticanus Graecus 1209 with many images.
• All-caps is harder to read]*Capitals] a Primer of Information About Capitalization With Some Practical Typographic Hints as to The Use Of Capitals by Frederick W. Hamilton, 1918, from Project Gutenberg
• Lower Case Definition]by The Linux Information Project; also includes information on lower case as it relates to computers.
• Case Converter, Online tool]