Learners' attempts to regulate their own motivation for studying in the face of tedious or difficult tasks is an important aspect of self-regulated learning. Therefore, motivation regulation has received increasing attention over the past few years, resulting in numerous publications using different definitions of the construct, samples, operationalizations, and research designs. The aim of this systematic review is to present an interactive evidence and gap map synthesizing current research with respect to what we know about motivation regulation, what the sources (e.g., samples, research methods, operationalizations) of this knowledge are, and which aspects proposed by theoretical models of motivation regulation remain understudied. Based on a systematic literature search, N = 289 studies were included. Approximately three quarters of the studies examined motivation regulation of university students, used cross-sectional study designs, and self-report questionnaires. Achievement, effort-related variables, (meta-)cognitive learning strategies, and goal orientations were the most frequently reported correlates of motivation regulation. Motivation regulation was examined mainly for learning in general, but also in more specific contexts, such as digital or foreign language learning. The maps' gaps reveal that we still know little about motivation regulation in pre- and primary school children and its development across school years. Furthermore, despite the conceptualization of self-regulation as a context dependent construct, contextual characteristics have received little attention. These and other gaps are discussed, including suggestions for advancing theoretical models of motivation regulation. The structured maps enable quick overviews of evidence (gaps), aiding a rapid, strategic development of future research questions and potential meta-analyses.