The Euler core is a numerical system written in C/C++. It handles real, complex, and interval values, and matrices of these types. Other available data types are sparse, compressed matrices, a long accumulator for an exact scalar product, and strings. Strings are used for expressions, file names etc. Based on this core, additional functions are implemented in the Euler matrix language, which is an interpreted programming language in the style of an advanced BASIC dialect. Euler contains libraries for statistics, exact numerical computations with interval inclusions, differential equations and stiff equations, astronomical functions, geometry, and more.