Sense of agency is the way in which we understand the causal relationships between our actions and sensory events. Agency is implicitly measured using intentional binding paradigms, where voluntary self-made actions and consequential sensory events are perceived as shifted closer together in time. However, a crucial question remains as to how we understand the relationship between others' actions and sensory events. Do we use similar binding processes as for our own actions? Previous attempts to investigate this phenomenon in others' have reached no clear consensus. Therefore, in an attempt to understand how we attribute the causal relationships between others' actions and sensory events, we investigated intentional binding in others' actions using an interval estimation paradigm. In a first experiment participants were required to make a button-press response to indicate the perceived interval between a self-made action and a tone, between a closely matched observed action and tone, and between two tones. For both self-made and observed actions, we found a significant perceived shortening of the interval between the actions and tones as compared with the interval between two tones, thus intentional binding was found for both self-made and observed actions. In a second experiment we validated the findings of the first by contrasting the perceived intervals between an observed action and tone with a matched visual-auditory stimulus and a tone. We again found a significant perceived shortening of the interval for observed action compared with the closely matched visual-auditory control stimulus. The occurrence of intentional binding when observing an action suggests we use similar processes to make causal attributions between our own actions, others' actions, and sensory events.