Metacognition and self-regulated learning (SLR) have been advocated by many and have significant support being seen as a potentially effective and low cost way of impacting learning. Fundamentally, the underlying supposition is that metacognition and SRL are important to learning, and thus raise attainment, and various studies have established that SRL, and in particular metacognition, has a significant impact on students' academic performance, on top of ability or prior achievement. However, there is some confusion around what the terms mean, with different authors defining them in different ways, and a lot of related terms, such as "learning to learn" and "higher order thinking skills" used as substitutes in often confusing ways. In fact, the scientific literature itself shows quite a bit of divergence in the ways the terms self-regulated learning and metacognition are used. This evidence review is comprised of two sections addressing the following questions: (1) What are metacognition and self-regulated learning? and (2) How can these skills be improved, and what impact does this have on attainment? [For the related guidance report, see ED612285.]