Coordinating conjunctions join elements of the same level: two words, two groups of words or two clauses that perform the same function. In a list, they connect nouns, adjectives or verbs: pan y queso, alto y fuerte, trabaja y estudia. They can also join complete sentences: Llegó temprano y abrió la tienda. Each part retains its independence; the conjunction only relates them. If the conjunction is missing, the parts are left separated and the phrase loses that relation of sum, contrast, alternative or correction. To see how the meaning changes according to the link, it is useful to compare them with other classes of Conjunciones and with the subordinating ones, which do not coordinate elements of the same level.

Y adds an element to another. Connects people, objects, actions or ideas without changing the logical order of the sentence: comí y dormí, libros y cuadernos, madre y padre. Before words that begin with i- or hi- the word e is used to avoid clashes in sounds: padre e hijo, salud e higiene, agua e hielo. The form changes only by the initial sound of the following word, not by its meaning. It is kept y in front of other vowels and in front of h when the word does not begin with the sound i: mesa y almohada, arte y historia. In long unions, y can coordinate two clauses and can also appear together with the Conjunciones correlativas when the sum is repeated in larger series.

O expresses alternative, choice or possibility. It presents two options and leaves the selection open: té o café, vienes o te quedas, hoy o mañana. Before words that begin with o- or ho- the form u is used to make pronunciation smoother: siete u ocho, madre u hormiga, esto u otro. The form changes only by the initial sound of the following word. u is not used before every vowel, only before o or ho at the start of a word. When the phrase offers more than two alternatives, the conjunction continues to mark each choice: casa, piso u oficina. In more complex sentences, the choice can be linked to Conjunciones subordinantes if an option depends on a condition or a prior decision.

Ni coordinates elements within a negative structure. It joins two words, groups or sentences and reinforces the negation already present: No vino ni llamó, ni frío ni calor, no quiere café ni té. It can also lead a negative sequence when the sentence begins with that idea: Ni tú ni yo sabemos la respuesta. In that case, the whole construction keeps a negative meaning. Ni does not introduce a neutral alternative like o; it eliminates options or adds them as absence. It appears frequently in repetitions of negation to add emphasis: No habla, no escucha ni responde. Its function fits well with broad negative structures and with the Conjunciones adversativas, because both deal with contrast or rejection, although ni does so from negation.

Pero connects two ideas that oppose each other in a gentle way. The first part sets up an expectation and the second limits it, corrects it or contrasts it: Quise ir, pero llovía; es pequeño, pero rápido. It is the most common form in conversation and in general writing. Mas expresses the same contrast, but sounds more formal or literary: quise ayudar, mas no pude. It is not commonly used in everyday speech. Both coordinating conjunctions connect elements at the same level, but pero appears in neutral registers and mas in more careful or expressive registers. For strong contrast, the language usually prefers other resources from Conjunciones adversativas, though pero remains the central form.

Sino appears after a negation to correct what was said before and to substitute one option for another: No quiero té, sino café; no estudia medicina, sino derecho. The first part denies a possibility, and sino introduces the correct or true one. It is not used to sum ideas nor to oppose two independent facts. The usual structure is negation + sino + corrected element. When the second part carries a verb, the full form can also correct an action: No vino ayer, sino hoy. In contrast to pero, which only contrasts, sino replaces. That corrective function relates to the opposition mechanisms of the Conjunciones adversativas and to the Conjunciones Causales when the sentence explains why one option is discarded.

Some coordinations use two particles spread through the phrase to present alternate or repeated options. Bien... bien offers two possibilities that alternate: bien llueve, bien sale el sol. Ya... ya marks alternation or succession: ya ríe, ya llora; ya en casa, ya en el trabajo. Ora... ora has a similar, more literary or elevated value: ora canta, ora calla. These pairs place one part before each coordinated element and maintain the idea of alternation throughout the construction. They do not join by sum, but by repetition of options. Their function is similar to that of other Conjunciones correlativas, because they distribute the relationship between two or more sentence segments.

Among long coordinate sentences, the comma helps separate the parts and read them clearly, especially when each sentence has its own subject, verb and complements: Llegó tarde al aeropuerto, pero alcanzó el vuelo. With y, o and ni the comma is usually omitted if the parts are short: Compró pan y leche. If the coordinate clauses are long or already carry internal commas, it is advisable to mark the pause with a comma before the conjunction: Terminó el informe, y después llamó a la oficina. With pero and sino the comma is very common when joining complete sentences. Punctuation does not change the coordinating relation; it just organizes the text better and avoids ambiguities, just as happens in other constructions with Conjunciones consecutivas or Conjunciones Comparativas when the phrase needs to clearly mark each segment.