In Spanish, the most common way to form a question is to invert the order of the subject and the verb. Question marks are also used at the beginning and end of the question. In short questions, the subject is sometimes omitted because the verb already indicates the person.

Closed-ended questions are answered with yes or no. They usually start with the verb or with a construction like Is... or Are.... The rising tone at the end also signals that it is a question, though in writing the inversion and the punctuation are what matter.

Open-ended questions use interrogative words to ask for information. These words carry an accent and typically appear at the start of the question. What follows is usually verb–subject inversion or a fixed structure depending on the wh-word.

The most common question words are what, who, when, where, how, which and why. Each introduces a type of information sought. They carry an accent in direct and indirect questions.

In Spanish, question words take an accent mark when they have interrogative or exclamatory value. This applies to both direct and indirect questions. Without the accent, the word may change meaning or function as another part of the sentence.

An indirect question does not carry question marks, but keeps the accent on the interrogative word. The usual structure is 'verb + if' for closed-ended questions or 'verb + interrogative' for open-ended. The order is not necessarily inverted as in direct questions.

'si' introduces an indirect closed-ended question and does not carry an accent. It is used to ask something that can be answered with yes or no within a larger sentence. It is different from 'sí' with an accent, which is the affirmation.

'Por qué' with an accent asks for the cause and is written separately. 'Porque' together and without the accent gives an explanation. 'Porqué' with an accent and together is a noun and goes with a determiner. 'Por que' separated can appear in less common structures.

In Spanish, intonation helps mark a question, especially in closed-ended questions. In writing, the structure and punctuation remain necessary, though intonation is key when speaking. In single-word questions, tone may be enough in conversation, but context remains important.

Spanish allows omitting the subject because the verb form indicates the person. In questions, this makes many phrases sound natural without stating the pronoun. It is used especially in informal registers and in contexts where the referent is already known.