Despite the importance of motivation in understanding the development and practices of reading, problems persist in how motivation-related constructs are defined and investigated. This article reports a concept analysis of how 12 terms have been used in current reading research. Selection criteria resulted in the identification of 92 data-based articles published in 28 peer-reviewed journals from 2003 to 2013. Over the period examined, there was a steady increase in the number of studies reported. Most were conducted in North America and Europe. Only 17% of the studies offered explicit definitions of the target constructs they examined. Another 64% relied on various forms of implicit definitions, and 19% provided no definitions of any kind. Usage problems frequently occurred as well. These included instances of vague associations among terms, occurring in 20% of the studies, synonymous reference to distinctly different constructs in 32%, and inaccurate statements made about constructs in 20%. Although a variety of motivation theories were used to ground the investigations, some 22% were essentially atheoretical. These difficulties were unrelated to the impact factor of the journals in which they appeared. Possible causes are discussed, together with suggestions for improvement.