We all experience boredom, from being stuck in airport security lines to reading poorly written book chapters. But what is boredom, why do we experience it, and what happens when we do? We suggest a new take on this everyday emotional experience, as an important and potentially useful cue that we’re not cognitively engaged in meaningful experiences. According to the Meaning and Attentional Components (MAC) model of boredom, people feel bored when they can’t successfully engage their attention in meaningful activities. Boredom can be painful, but it gives us important feedback about our lives, by signaling a lack of meaningful attentional engagement. In short, boredom tells us whether we want to and are able to focus on what we are doing or thinking, and steers us towards behaviors that ensure that we do. Across a broad range of situations, attention and meaning independently predict boredom, are not highly correlated, and do not interact. But more importantly, attention and meaning deficits result in different types of boredom with different downstream consequences for how people behave. For instance, being bored because what you’re doing lacks meaning feels different and has different consequences than being bored because you can’t pay attention, in part because they signal different problems. Likewise, boredom can result when something is too easy or too hard, because both make it hard to pay attention. All of these different causes of boredom matter, we argue, because they result in different types of boredom with different downstream consequences. Why we are bored shapes what we want to do next, and helps explain why bored people make often puzzling decisions, such as choosing to self-administer painful electric shocks or turning to political extremism. In short, like pain, boredom may be unpleasant but it plays an important role in alerting us when we either don’t want to (or are unable to) pay attention to what we’re doing, and motivating us to change our behavior to restore attention and meaning to our lives, for good or for ill.