A growing body of research has begun to address ethical issues in the context of Applied Linguistics (e.g., De Costa, 2016; Isbell et al., 2022). One of the messages inherent in this line of inquiry is that ethical concerns are embedded throughout the research cycle from study conceptualization to realization, dissemination, application, and beyond (see Bernstein et al., this volume). With this concern in mind, the present study sought to catalog and develop a taxonomy of what are often referred to as ‘questionable research practices’ (QRPs; Steneck, 2006) and related decisions that come into play in the conduct of quantitative Applied Linguistics research. These include practices such as selective reporting and obscuring of methodological details to limit criticism. Using existing taxonomies developed in neighboring disciplines as a starting point (e.g., Tauginienė et al., 2019), we employed the Delphi method to elicit responses on potential QRPs in an iterative fashion from an expert panel as well as from peer scholars. The analyses of these data resulted in a domain-specific taxonomy that laid the groundwork for a large-scale survey that assessed the prevalence and perceived severity of ethical issues and QRPs found specifically in quantitative Applied Linguistics research (Larsson et al., 2023). The results are also used to inform materials for methodological training in research ethics in Applied Linguistics and related disciplines (see De Costa et al., 2021; Wood et al., 2024, in press).