The conditional mood (abbreviated cond) is a grammatical mood used in conditional sentences to express a proposition whose validity is dependent on some condition, possibly counterfactual.

It may refer to a distinct verb form that expresses the conditional set of circumstances proper in the dependent clause or protasis (e.g. in Turkish or Azerbaijani), or which expresses the hypothetical state of affairs or uncertain event contingent to it in the independent clause or apodosis, or both (e.g. in Hungarian or Finnish). Some languages distinguish more than one conditional mood; the East African language Hadza, for example, has a potential conditional expressing possibility, and a veridical conditional expressing certainty. Other languages^[which?] do not have a conditional mood at all.^{[citation needed]} In some informal contexts, such as language teaching, it may be called the "conditional tense".

Some languages have verb forms called "conditional" although their use is not exclusive to conditional expression. Examples are the English and French conditionals (an analytic construction in English, but inflected verb forms in French), which are morphologically futures-in-the-past, and of which each has thus been referred to as a "so-called conditional" (French: soi-disant conditionnel) in modern and contemporary linguistics (e.g. French je chanterais, from Late Latin cantāre habēbam, in si vous me le permettiez, je chanterais, "if you allowed me to do so, I would sing" [so-called conditional] vs. j'ai dit que je chanterais, "I said that I would sing" [future-in-the-past]). The English would construction may also be used for past habitual action ("When I was young I would happily walk three miles to school every day").

This article describes the formation of the conditional forms of verbs in certain languages. For fuller details of the construction of conditional sentences, see Conditional sentence (and for English specifically, English conditional sentences).

English does not have an inflective (morphological) conditional mood, except in as much as the modal verbs could, might, should and would may in some contexts be regarded as conditional forms of can, may, shall and will respectively. What is called the English conditional mood (or just the conditional) is formed periphrastically using the modal verb would in combination with the bare infinitive of the following verb. (Occasionally should is used in place of would with a first person subject – see shall and will. Also the aforementioned modal verbs could, might and should may replace would in order to express appropriate modality in addition to conditionality.)

English has three types of conditional sentences, which may be described as factual ("conditional 0": "When I feel well, I sing"), predictive ("conditional I": "If I feel well, I shall sing"), and counterfactual ("conditional II" or "conditional III": "If I felt well, I would sing"; "If I had felt well, I would have sung"; or "Were I well (if I were well) I would have sung"). As in many other languages, it is only the counterfactual type that causes the conditional mood to be used.

Conditionality may be expressed in several tense–aspect forms. These are the simple conditional (would sing), the conditional progressive (would be singing), the conditional perfect (would have sung), and conditional perfect progressive (would have been singing). For the uses of these, see Uses of English verb forms. The conditional simple and progressive may also be called the present conditional, while the perfect forms can be called past conditional.

For details of the formation of conditional clauses and sentences in English, see English conditional sentences.