The Spanish imperfect progressive is very similar to its English counterpart (was + -ing). In both languages, the imperfect progressive expresses an action that was in progress in the past when it was interrupted by another event.
|Estaba estudiando cuando llamaste.||I was studying when you called.|
|Lo vi cuando estábamos caminando.||I saw him when we were walking.|
|¿Estabas leyendo ahora mismo?||Were you reading just now?|
|Él estaba trabajando a las siete.||He was working at seven o’clock.|
The imperfect progressive is similar in usage to the imperfect, but with an emphasis on the fact that the action was in progress at the moment it was interrupted.