The gerund (gerundio) is a special, invariable form of the verb which always ends in -ndo in Spanish, for example: hablando, comiendo, viviendo. An alternate name for it is simply “the -ndo form”. In English it is translated as the “-ing” form of the verb (for example, “speaking”), which has lead to the frequent mistake of calling this form the “present participle”. The gerund is a verb form which has an adverbial function ,not an adjectival function like a participle, nor a noun function like an infinitive.

Forms:

To form the gerund, remove the infinitive ending (-ar, -er, or -ir) of a verb and add -ando for -ar verbs, and -iendo for -er and -ir verbs:

• caminar > caminando
• volver > volviendo
• abrir > abriendo

Verbs of the second and third conjugations for which the stem ends in a vowel, change the ending -iendo to -yendo:

• leer > leyendo
• caer > cayendo

The gerund for the verb ir is yendo.

Third conjugation verbs with stem changes:

Those which have the changes o>ue>u [e.g., dormir, duermo, durmió] use that u which appears in preterit third-persons forms in the gerund:

• dormir > durmiendo
• morir > muriendo

Those which have the changes e>ie>i [e.g., sentir, siento, sintió] use that i which appears in preterit third-persons forms in the gerund:

• sentir > sintiendo

Those which have the changes e>i>i [e.g., pedir, pido, pidió] use that i which appears in preterit third-persons forms in the gerund:

• pedir > pidiendo

The gerund is primarily used: with estar to form the progressive tenses; with verbs of motion and seguir/continuar; to introduce an adverbial phrase or express “by (do)-ing (something)”.

To form a progressive tense, use the appropriate tense of the verb estar immediately in front of the gerund, e.g.:

• No me molestes; estoy trabajando.
  Don't bother me; I'm working.
• Estábamos almorzando cuando llegaron.
  We were eating lunch when they arrived.
• Estuvimos haciendo ejercicio por tres horas.
  We were exercising three hours [Or: We spent three hours exercising.]
• Dudo que estén practicando a esta hora.
  I doubt they're practicing at this hour.

Note that any tense can be used to form a progressive, even the preterit as given in the third example above [note that there the action is viewed as having been limited to a three hour period]. However, the present and imperfect tenses the ones most frequently seen.

Caution: As the name indicates, the progressive tenses express an action viewed as being in progress. Do not use the progressive for other purposes, such as for expressing a future action: “We're leaving for Mexico tomorrow” (Salimos para México mañana [NOT Estamos saliendo).

To express the idea “to continue (to do something)” or “to keep on (doing something)”, use seguir or continuar with the gerund:

• Sigo teniendo problemas con mi computadora.
  I keep on having [continue to have] problems with my computer.
• Continúan haciendo las mismas preguntas.
  They keep on asking the same questions.

Note that the stem vowel in continuar is the weak vowel u, so it needs a written accent in the form used above.

Numerous verbs of motion may also be used with the gerund, for a variety of effects or purposes. Please note the uses of entrar, salir, venir, and andar given below:

• Marcos salió (de la casa) corriendo.
  Marcos went running (out of the house). [O: Marcos ran out ...]
• Mi hermana entró llorando.
  My sister came in crying.
• Luego ellos vinieron pidiendo más dinero.
  Then they came along asking for more money.
• Ese tipo anda quejándose de todo.
  That guy goes around complaining about everything.

To express “by (do)-ing (something)” when it comes after a verb, normally the gerund is used :

• Ella ganó miles de dólares escribiendo cuentos cortos.
  She earned thousands of dollars by writing short stories.
• Mejoré mi técnica como violista practicando ocho horas al día.
  I improved my technique as a violinst by practicing eight hours a day.
• Perdieron el partido haciendo un error increíble...
  They lost the game by making one incredible mistake...

Note that the this idea is not expressed by preposition por plus an infinitive. Por used in that way means things like “because of (do)-ing (something)” or “for the sake of (do)-ing (something)”:

• Salió por ser cobarde.
  He left because of being [because he was] a coward.

The gerund can also be used to introduce a phrase with a “by the way”-type meaning, or causal (“because” or “since”) or temporal (“while”, “when”) meanings:

• Hablando de vacaciones, ¿qué vas a hacer este verano?
  Speaking of vacations, what are you going to do this summer?
• Sabiendo qué hacer, pude entrar en la oficina sin que nade me viera.
  Knowing [because I knew] what to do, I was able to get into the office without anybody seeing me.
• Camindo por el pueblo, noté que nadie estaba en las calles.
  [While / When I was] walking through the town, I noticed that nobody was in the streets.

After verbs of perception —for example, ver, mirar, notar, oír, escuchar— the gerund (or the infinitive) may be used to describe how or when the action is being performed.

• Ayer vi a Elena caminando por el parque.
  Yesterday I saw Elena [as whe was] walking through the park.
• ¿Has oído a tu marido cantando en la ducha?
  Have you heard your husband singing in the shower?
• Habrás notado los muchos gansos caminando por nuestra ciudad universitaria.
  You've probably noticed the many geese walking around our campus.

A few things mentioned above may need to be repeated:

The gerund is a verb form with an adverbial function; do not use it as a noun. Use the infinitive as the object of a preposition or as the subject of a verb:

• después de descansar = “after resting”
• Leer es divertido = “Reading is fun”

Do not overuse the progressive tenses, since they are used far less frequently in Spanish than in English, and do not use them unless you are portraying an action as truly being in progress.

Remember that “by (do)-ing (something)” is normally expressed with the gerund and not por + infinitive [which means “because of (do)-ing (something)” or “for the sake of (do)-ing something”.