Research in mathematics education has investigated teachers' professional knowledge in depth, comprising two different approaches: a cognitive and a situated perspective. Linking these two perspectives leads to addressing situation-specific skills such as perception, interpretation and decision-making, indicative of revealing a teacher's knowledge while in the act of teaching. The aim of this study is to systematically review empirical research into mathematics teachers' situation-specific skills. From the databases ERIC, PsycINFO and MathEduc a total of 60 articles were included in the review, based on specific criteria. The studies were categorized with respect to theoretical frameworks used, designs and methods applied as well as the main findings of each study. Teachers' noticing or teachers' professional vision, and teachers' (situated) professional knowledge were found to be the most frequent frameworks. Designs ranged from comprehensive case studies with a variety of methods to confirmatory studies testing a large sample with standardized instruments. The main findings suggest: (1) Teachers' expertise and experience positively influence noticing and teachers' noticing can be successfully fostered by (video-based) professional development programs. (2) Pre-service teachers struggle with perceiving and interpreting students' work. Thereby, their mathematical knowledge plays an important role. (3) Teachers' in-the-moment decision-making is influenced by their knowledge, beliefs and goals. (4) Teachers' knowledge and belief facets predict their situation specific-skills which in turn correlate with aspects close to instructional practice. (5) Teachers have difficulties interpreting tasks and identifying their educational potential. Methods and implication of this systematic review are thoroughly discussed.