Language development is a long-term process. Individual-level longitudinal case studies have been foundational to SLA. However, methodologies that can support person-focused and process-oriented research lack consolidation. Qualitative longitudinal (QL) research (Neale, 2021a, 2021b) is a methodology that facilitates exploration of the influences of time over time. It provides a temporal architecture within which the ever-changing influence of time can be explored. In QL research, development is studied during a period of transition. With focus trained on a defined time window, data generation is guided by temporally configured strategies. This article introduces QL methodology and demonstrates its application in the investigation of willingness to communicate (WTC) among immigrant women in Sweden. We present the key principles of QL research, and the application of data collection strategies that are (1) sequential, (2) participatory, (3) cartographic, and (4) recursive. In QL research, exploration of the episodic and incremental nature of change will be facilitated when narratives reflecting a participant’s experiences are compiled and shared with an engaged researcher in sequentially ordered interviews. In a QL study, time provides an axis of comparison. With participatory data providing pivots around which an interview is conducted, interviews are designed to map out temporal shifts. In mapping a developmental journey, events currently in focus are examined in relation to similar events discussed in preceding interviews and, within broader developmental timeframes, previous journeys. The article concludes with an assessment of the opportunities and challenges associated with QL research. © 2024 The Author(s)