This chapter introduces the corpus-based L2 French phonology research programme Interphonologie du Français Contemporain (IPFC, Interphonology of Contemporary French) and provides an illustration of its methodological approach with a population of Spanish university students learning French as an L2. For these learners the phonemic contrast between the two close rounded French vowels /y/ and /u/ is known to be difficult to acquire, but most studies in the past relied only on acoustic analyses of laboratory speech data elicited from rather few subjects. Within the IPFC framework, on the basis of a single multitask survey protocol for all populations of learners of L2 French to ensure data comparability, data processing is carried out with an ad hoc auditory coding procedure which integrates contextual information and target-likeness assessment. In this chapter we compare the results of three different approaches to process the /y-u/ Spanish production data: non-expert native perceptual evaluation, IPFC coding procedure, and acoustic analyses. The results are discussed in light of the current development of L2 corpus phonology.