This chapter discusses the nature of numeracy, which is concerned with the use of mathematics in context, reflecting some recent Australian work concerned with numeracy across the curriculum, and some Australian initiatives to highlight mathematics in wider contexts than the mathematics classroom. Australian national curriculum developments, in which numeracy is identified as a General Capability to be addressed in all school curricula, not only in mathematics curricula, are described. In the primary years, situations that demand some level of mathematical thinking arise in all aspects of the curriculum, sometimes unexpectedly, and thus provide opportunities for numeracy to be developed providing we are alert to the possibilities, while in the secondary years, mathematics is important for learning in other subjects, although this is not always well recognized. Students need to develop a capacity to use mathematics in their everyday lives, their school lives and eventually in the world of work. The chapter explores examples of numeracy demands and opportunities across the curriculum, and considers the roles of teachers to develop the necessary mathematical, contextual and strategic expertise to address these.