Functions are used in every branch of mathematics, as algebraic operations on numbers, transformations on points in the plane or in space, intersection and union of pairs of sets, and so forth. Function is a unifying concept in all mathematics. Relationships among phenomena in everyday life, such as the relationship between the speed of a car and the distance travelled, are functions. The concept of function has an important part in the school mathematics curriculum; yet, many countries today are concerned with how to structure the curriculum. The first part of this brief provides a short background about the historical development of function in mathematics and its introduction into the school curriculum, explicating the "identity crisis" many countries are facing today. I then elaborate more on the goals for including functions in the school curriculum and on the learning about functions. I conclude this brief with challenges that policy makers, curriculum developers and teachers face and possibilities for meeting these challenges.