This study was an attempt to integrate motivation into reading comprehension, with active knowledge construction as a linkage. The study examined two motivational constructs, need for cognition and reader's beliefs, in terms of their role in text comprehension and interest development. The results of the study provided empirical evidence for the independent contributions of the two variables to reading comprehension. Furthermore, the results suggested that effects of these variables on comprehension cut across expository and narrative genres. The study further explored direct and mediated effects of need for cognition and transaction belief on topic interest and the possible mediational role of comprehension. Strong effect sizes of relations found between these variables support the notion of motivational processes as an integral part of effective text comprehension, and suggest the dynamic interplay of reader characteristics, comprehension activity, and interest development.