Apart from providing a bird's eye view of a given domain of inquiry (Ioannidis et al., 2015), systematic reviews such as methodological syntheses offer a magnifying glass on prevalent existing problems in primary research and furnish empirically grounded solutions to rectify these issues (Page et al., 2021). As survey research in second language acquisition grows in popularity, especially in the substantive domain of individual differences, the adherence to best practices associated with study and questionnaire design alongside reporting practices related to transparency is critical for a better understanding of factors that influence second language (L2) development. To ensure that a self-report scale designed to measure a latent construct such as anxiety and willingness to communicate (WTC) indeed targets the construct of interest and does it consistently and accurately, authors of primary research should demonstrate that their instrument possesses acceptable psychometric properties (i.e., evidence of validity and reliability) and is suitable to use with their chosen population of L2 learners or teachers. However, previous studies have raised concerns about the psychometric properties of questionnaires in L2 research (Al-Hoorie & Vitta, 2019; Gu, 2016). Building on works such as Plonsky (2013, 2014) and Sudina (2021), this methodological synthesis focuses on the state of study and scale quality in L2 anxiety and WTC research by examining key methodological issues of quantitative survey research and offering empirically grounded suggestions for future studies. The scope of the study is confined to a total of 232 peer-reviewed articles that used 385 L2 anxiety and WTC scales and were published in 22 leading applied linguistics journals over a 20-year period. The search channels for locating and retrieving eligible studies included journal websites, the Second-language Research Corpus (Plonsky, n.d.), and two databases: Linguistics and Language Behavior Abstracts (LLBA) and PsycINFO. Features targeting sample, survey, and scale characteristics and reporting practices at both the study and scale levels have been examined in depth as well as compared over time. Particularly problematic is the lack of evidence for scale content and construct validity--including testing for measurement invariance and referring to previous validation studies for existing scales--as well as reporting rates of survey responses and missing data. The results and implications of this study contribute to concurrent attempts at methodological reform in applied linguistics and aim to promote ethically appropriate research practices. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]