English interjections are a category of English words – such as yeah, ouch, Jesus, oh, mercy, yuck, etc. – whose defining features are the infrequency with which they combine with other words to form phrases, their loose connection to other elements in clauses, and their tendency to express emotive meaning. These features separate English interjections from the language's other lexical categories, such as nouns and verbs. Though English interjections, like interjections in general, are often overlooked in descriptions of the language, English grammars do offer minimal descriptions of the category.

In terms of their phonology, English interjections are typically separated from the surrounding discourses by pauses, and they can contain sounds not otherwise found in English. English interjections tend not to take inflectional or derivational morphemes. In terms of their syntax, they tend not to form constituents with other words and are parenthetical rather than integrated into the clauses in which they occur. Semantically, they often have emotive or interpersonal meanings and their use is sometimes called exclamatory. English interjections fill several pragmatic roles in English, including greeting and indicating agreement.

In 1586, William Bullokar wrote the earliest grammar of English, which included a small section on interjections. His definition of English interjections focused on the semantic and pragmatic dimensions of the words:

An interjection is a part of speech that betokeneth a sudden passion of the mind: the signification or meaning of which speech much be understanded by the gesture, countenance, or passion of the speaker, and some time with regard of the person spoken to, or of the thing spoken of.^[1]: 373 (orthography has been modernized)

In 1795, Lindley Murray offered a definition of English interjections that made note of their syntactic properties in addition to their pragmatic properties, defining them as "words thrown in between the parts of a sentence to express the passions or emotions of the speaker: as, 'Oh! I have alienated my friend; alas I fear for life:' 'O virtue! how amiable thou art!'"^[2]: 119

In the early twentieth century, Otto Jespersen rejected the idea that English interjections are a lexical category at all, treating interjections instead as a manner in which words of other lexical categories may be used (such as the noun Fiddlesticks! and the verb Come!).^[3]: 90

Later in the twentieth century, A Comprehensive Grammar of the English Language included interjections in its list of word classes but conceded that they are a "marginal and anomalous class."^[4]: 67 It also noted that interjections differ from similar word classes in that "they are grammatically peripheral, in the sense that they do not enter into constructions with other word classes, and are only loosely connected to sentences with which they may be orthographically or phonologically associated."^[4]: 74

In their Student's Introduction to English Grammar, Rodney Huddleston and Geoffrey K. Pullum omit interjections from their list of lexical categories because, in their view, "there really isn't anything interesting for a grammar to say" about interjections.^[5]: 16

Though the number of traditionally recognized English interjections is relatively small compared to other lexical categories, nonce interjections can be freely created through onomatopoeia.^[4]: 74 Thus, a complete list of English interjections is impossible. However, very common interjections can be listed. The most frequent words tagged as interjections in the Corpus of Global Web-Based English (GloWbE)^{[upper-alpha 1]} include yes, no, oh, yeah, hi, hey, wow, hello, ah, ha, blah, eh, yep, o, alas, haha, cheers, huh, and hmm.^[6]

From the point of view of pragmatics, English interjections typically have exclamatory or imperative force; for example, ouch! is an exclamation expressing the speaker's pain and hush! issues a demand for the addressees to become silent. However, they can also be used to convey statements and questions (such as in uh-huh and eh?, respectively).^[4]: 88 English interjections can be used to greet people or call attention (e.g., hey, hello), show agreement (e.g., yes, amen, okay) or disagreement (e.g., no, uh-uh), indicate understanding (e.g., oh, uh-huh) or lack thereof (e.g., huh), demand silence (e.g., sh), make a polite request (e.g., please), show disinterest (e.g., meh), or even invoke magic (e.g., abracadabra).^[19]

Many of the most common English interjections (see § Typical examples) are primarily involved in interactions between users of the language, maintaining the integrity of the conversation through backchanneling and marking affirmation.^[21] For example, a listener may say "yeah" or "uh-huh" to signal their attention to and understanding of a speaker's words.

Semantically speaking, English interjections do not refer; that is, while other lexical classes like nouns and verbs typically reference particular participants or processes that exist or could exist in the world, English interjections tend to merely express the internal states of their users.^[22] Many express emotions such as anger (e.g., damn), disgust (e.g., eww, yuck), surprise (e.g., wow), regret (e.g., alas), or embarrassment (e.g., shucks).^[19] They can also signify pain (e.g., ow), bad smells (e.g., pew), a mistake (e.g., oops), or a sudden realization (e.g., eureka).

English interjections tend not to inflect or form through derivation.^[8]: 106 Some other lexical categories in English also tend not to inflect but still carry inflectional morphemes associated with other categories; for instance, English prepositions tend not to inflect, but the prepositions barring and concerning contain remnants of the -ing suffix of present participle verb forms.^[4]: 669 The same is true of English interjections. For example, the interjections heavens and bollocks contain remnants of the plural -s inflectional suffix from when they were nouns.^[19]

Phonologically, English interjections or interjection phrases are often supplements and, as such, are typically separated by a pause from the other utterances with which they may co-occur, constituting a prosodic unit by themselves.^{[8]: 108 [9]: 25} This disruption to the typical prosody of the clause is represented in writing through punctuation – such as commas, dashes, and parentheses.^[9]: 67 For instance, the dash in the previous sentence marks such a disruption.

English interjections may exhibit phonological features that are not typical of the language. For example, the interjection uh-oh (IPA: [əʔo]) is a rare case of a glottal stop in dialects of English that otherwise lack such stops.^[23] Other examples of English interjections containing phonemes not normally found in English include the denti-alveolar clicks in tut-tut (IPA: [ǀǀ]), the voiceless bilabial fricative in whew (IPA: [ɸɪu]), and (for dialects that no longer use it) the voiceless velar fricative in ugh (IPA: [əx]). Spelling pronunciations often emerge for interjections that feature these atypical phonemes, including /tət tət/ for tut-tut and /əɡ/ for ugh.^[4]: 853

Use of interjections varies over time and between speaker groups.

Geographical variation can be seen in the use of interjections like lah, which are found almost exclusively in Singapore and Malaysia in the GloWbE corpus,^[24] yaar, which is almost entirely limited to India and Pakistan,^[25] or haba, which is almost entirely limited to Nigeria.^[26] Variation can also exist among speaker groups within one area. For example, the interjection word indicating agreement is characteristic of African-American English.^[27]

Two examples of variation over time can be seen in the Corpus of Historical American English, which shows that nay was among the most common interjections in 1820 but by the 2010s had become significantly less common.^[28] In contrast, yeah does not occur in the corpus in 1820, but is among the most used interjections by the 2010s.^[29]