Learning a third language (L3) in school is a common experience for students in countries all over the world, particularly in Europe where a central aim of European Union educational policy is the development of multilingualism (Cenoz & Jessner, 2000; European Commission, 2005, 2008). Common language combinations, as for example in the Scandinavian countries, are English as the initial instructed foreign language (the L2) with French, German or Spanish (the L3) introduced at a later stage. The simultaneous learning of more than one foreign language (FL) has begun to attract the interest of motivation researchers, with findings pointing to the popularity of English (Csizér & Dörnyei, 2005; Csizér & Lukács, 2010) and indicating that, comparatively, motivational trajectories for L3s show a markedly steeper decline (Henry, 2009). There is also evidence that L3 motivation is prone to greater fluctuation, both gradual and dramatic (Mercer, 2011) and that, in competition for the learner’s time and resources, L2 English can have negative effects on L3 motivation (Henry, 2010, 2011, 2014; Mercer, 2011).

   As Cameron and Larsen-Freeman (2007: 227) note, complexity theory approaches that reject linear scenarios and focus on the webs of interactions taking place within and between dynamic systems, seem to resonate with ‘the problem spaces of applied linguistics’. One particular ‘problem space’ where complex dynamic systems (CDS) theories can usefully be applied is in third language acquisition. The acquisition of a third language involves greater degrees of complexity than in situations when only one new language is in focus as it is necessary to account for the interactions between different language systems in the learner’s mind (Herdina & Jessner, 2002; Jessner, 2006, 2008). This means that, in addition to all of the individual difference factors recognised in SLA, in third language acquisition the evolution of a language system will also be dependent on the development and behaviour of other parallel language systems (Jessner, 2008).    

   With the aim of examining the motivational dynamics of six Swedish students learning French as an L3, this chapter reports on findings from a series of semi-structured interviews and classroom observations conducted over a nine-month period. The chapter begins with an overview of some of the CDST concepts used when engaging with the data, and concludes with a reflection on some of the methodological challenges encountered in this type of research.