The paper aims to point out some limitations of quantitative methods in multilingualism research and to highlight some advantages of qualitative methods which can help to counterbalance those limitations. However objective and rigorous quantitative methods seem to be, they cannot fully account for the complex, dynamic and variable nature of multilingual systems, as they involve some inevitable simplifications, such as measuring reaction times in single-word experiments, or the numerical encoding of responses on the basis of the researcher's linguistic competence.It is thus advisable, following Dörnyei (Research Methods in Applied Linguistics. Quantitative, Qualitative and Mixed Methodologies. Oxford University Press, Oxford, 2007), to use mixed methods which combine some quantitative analysis (not necessarily statistics, but also the numbers of instances of transfer (Pavlenko and Jarvis. Applied Linguistics 23:190–214, 2000) or percentages (Gabryś-Barker. Aspects of Multilingual Storage, Processing and Retrieval. Wydawnictwo Uniwersytetu Śląskiego, Katowice, 2005; Wlosowicz. Cross-linguistic interaction at the grammatical level in L3 comprehension and production. In Cross-linguistic Influences in Multilingual Language Acquisition, ed. Gabryś-Barker, pp. 131–150. Springer, Heidelberg, 2012)) and qualitative methods, such as the analysis of numerous examples from think-aloud protocols which illustrate actual language processing. Moreover, given the importance of individual language biographies for multilingual proficiency, an important qualitative research tool is the collection and analysis of personal narratives (Todeva and Cenoz eds. The Multiple Realities of Multilingualism. Personal Narratives and Researchers' Perspectives. Mouton de Gruyter, Berlin/New York, 2009b). In fact, not only studies which focus on narratives as such, but also other studies on multilingual language processing and use should take into account some biographical data, for example, by asking about them in the questionnaires, besides such "target" information as lexical associations, grammatical problems, etc. It is concluded that quantitative and qualitative studies should complement each other in order to yield a more complete picture of multilingual language organization and processing.