What is boredom? We present a new model in which boredom is an affective indicator of unsuccessful attentional engagement in valued goal-congruent activity. Boredom consists of (a) an attentional component, or mismatches between cognitive demands and mental resources and (b) a motivational component, or mistmatches between activities and valued goals. In two correlational studies (Study 1 n = 245; Study 2 n = 110), participants sitting alone in a room with just their thoughts were more bored when they reported attentional difficulties than attentional success, ds = .86, .80, ps <.001, and when their thoughts were low on personal meaningfulness, ds = .81, .73; ps <.001. In Study 3 (n = 217), experimentally manipulating attention and meaning on an air traffic control task independently induced boredom, ds = .33, .35; ps = .016, .013, and did so via separate mechanisms. The interaction between attention and meaning was not significant in any of the studies, all ps > .37.