In this chapter we present the Arithmetic Black Box (ABB) functionality. It is an ideal functionality that preserves the privacy of the data it stores and allows computations to be performed on the data stored, as well as retrieve certain pieces of data. We show that it is a very convenient abstraction of secure multiparty computation (SMC), which enables easy extensions and the construction of large privacy-preserving applications on top of it. In this chapter, we give a detailed definition of the ABB functionality and present different ways in which it can be implemented securely. We explain what extending an ABB means and how it is integrated into larger applications.