In this chapter, I have given a critical account of motivation research in the field of AL. Due to the great extent of research output, I have primarily focused on works relevant to my research focus as well as my research context. On the whole, there have emerged five focal matters pertinent to the understanding of the target construct. First, motivation is intricately connected to other psychological processes, namely, cognitive and emotional ones. The former have typically been conceptualized as goal orientations (Gardner, 1985; Ryan & Deci, 2000, 2020), future self-conceptions (Dörnyei, 2005, 2009a; Kubanyiova, 2009), perceptions of self-competence (Bandura, 1995; Ryan & Deci, 2000, 2020), and values (Gardner, 1985). I have consistently argued that emotions have been afforded only marginal attention in the study of motivation in AL; most notably, they have been featured in the multidimensional concepts, linguistic self-confidence (Clément, 1980) and language attitude (Gardner, 1985). While empirical research on L2 learning motivation has been gradually making up for this limitation, still, overall, there seems to be a long way to go to explore the emotional dimension of motivation in light of some taxonomies of emotions in educational psychology (e.g., Pekrun, 2014; Pekrun et al., 2007). Second, motivation has also been consistently linked to social processes. This indicates that it does not occur in vacuum, and that motivation can only be truly grasped by also considering the various contextual layers in which humans are embedded (see, e.g., Dörnyei, 1994; Gardner, 1985; Williams & Burden, 1997). Third, it also transpires that motivation is a gradable human experience (Dörnyei & Ushioda, 2013). As such, it can manifest itself in different levels of strength, a result of the positive or negative influences of the earlier-mentioned processes. Fourth, motivation is likely to be subject to fluctuations. While, in earlier theoretical models, it was conceived of as a linear process (e.g., Clément, 1980; Dörnyei, 1994; Gardner, 1985), such an assumption has gradually become outdated (Dörnyei, 2005, 2009a). Finally, motivation can be broken down into at least two distinct phases. One relates to a person’s decision to engage in action, the other to one’s actual engagement in it (Dörnyei & Ottó, 1998; Dörnyei & Ushioda, 2013).