After a historical overview of the effort topic in translation and interpreting (Translation) studies, the authors discuss the relation between effort and Translation performance and argue that effort investment is not only a technical matter but also an ethical issue. They then zoom in on cognitive effort, with explanations on the concept and an overview of research on the topic, including behavioural and physiological methods used to measure cognitive effort in translation and interpreting tasks. The final part of the chapter offers a discussion of methodological challenges associated with the use of the concept of cognitive effort and its measurement.