This document describes key stages in the development of the Numeracy assessment scale for the ALL survey that took place between 1998 and 2003.  The authors present a conceptual discussion of the numeracy construct and its facets, examines approaches to assessment of mathematical skills, and reviews issues that influenced the item development process. This conceptual discussion had a large influence on the development of the numeracy framework for the PIAAC assessment. Included in the document are appendices which contain sample numeracy items that have been released to the public and details of a scheme of complexity factors that was used to inform the evaluation of difficulty levels of items. The complexity factors could be useful when teachers develop assessment tasks for their own students.