As SLA diversifies in scope and scale, key questions remain open over the nature, development and use of a second (or third and additional) language. In this chapter, we evaluate the use of specific methods for different paradigms, while making the case for building inclusive and transdisciplinary connections to sustain the strength of the field. The chapter starts with research methodologies for investigating the development of L2 morpho-syntactic knowledge, as the traditional foundation of SLA. We distinguish between internal formal/cognitive questions around L2 linguistic representation and processing, typically focusing on group trends in quantitative findings, and external socially mediated research into L2 use, often focusing on exploratory individual experiences and motivation through qualitative data. We then present research into L2 phonology (L2 speech), complementing L2 morphosyntax in its focus on form, but often neglected in coverage of SLA research methodology. We finish by looking at implications for future SLA research, driven by greater interest in methodological rigor, replicability and open science, and the opportunities provided by the technological and social media revolution of recent years, e.g., using corpora, online/mobile platforms, and big data.