As humans are social by nature, our every day behavior is greatly influenced by each other. Whether we compete or cooperate with others, we have to take into account their behavior when deciding a course of action of our own. An understanding of the intentions or goals of other humans would serve this purpose, because it allows to make predictions about how their actions will evolve. Hence, the ability to infer the goals of others by observing their behavior is very useful to us. Furthermore, copying the goals of other beings around us can be useful as well. For instance, when another individual wants to cooperate with us, it can be greatly beneficial to reciprocate his behavior with a similar cooperation goal. In social psychological research it has recently been demonstrated that copying a goal from another person can even occur outside our awareness, a phenomenon that has been termed goal contagion. The current thesis investigates this phenomenon, by studying several conditions under which it may or may not occur. Also, the underlying cognitive mechanisms that are responsible for goal contagion are mapped based on current models of the human mental system. Whether people catch on the goals of others may by dependent on a variety of factors, for instance the person we are observing, the goal that we infer from his behavior, or the circumstances we find ourselves in. This thesis focuses on a characteristic of the behavior that we observe, which is the amount of effort that someone invests in his behavior. As more effortful behavior represents more willingness to attain a goal, perceiving effort signals to observers that the goal the other is after is worthwhile, and hence triggers our interest. In a total of nine experiments, the current research shows that observers become more motivated to find out the goal that another is pursuing, when this other invests more effort in his behavior. Furthermore, people are more likely to make a spontaneous inference about the goal of another, when his behavior contains more effort. This leads to an greater adoption of the goal by observers, that is, they are more likely to copy a goal when they see it is pursued with more effort. Lastly, it was demonstrated that people’s motivation to attain a goal is directly influenced by the effort that another individual invest to attain that goal, without their awareness. Interestingly, these results were found even when the behavior was performed by a non-living object. After exposure to an animated film in which the ‘actor’ was a moving ball, participants copied its goal. The implications of the results above are discussed in relation to theories about social influence and unconscious processes in general.