Most everyday number processing involves multi-digit numbers (e.g., money, prices, times, dates). However, much of the research in the field has so far focussed on single-digit number processing. Whilst some basic cognitive effects obtained this way transfer to multi-digit numbers, other cognitive mechanisms cannot be studied using single-digit material. Thus, multi-digit number processing and its cognitive consequences have recently moved more into the focus of scientic attention. This volume outlines commonalities and differences in related aspects of multi-digit number processing to highlight this important subfield of numerical cognition research.