Engineers, physicists, and mathematicians consider many of the same ideas and techniques, but often express them in quite different languages. This chapter establishes some of the standard language, notations, and conventions of mathematics. It makes the readers to find it useful in understanding the text itself and that it will help scientists appreciate why mathematicians must be so fastidious. The basic objects in mathematics are sets and functions. A set is a collection of objects. These objects are called the elements or members of the set. Mathematicians use the word well-defined to mean that it makes logical sense to define the object. The words variable, constant, and parameter arise throughout the sciences. Their usage changes with the context, and hence seeking precise definitions of the terms is hopeless. Nonetheless, the following remarks and examples might be useful. The chapter closes by discussing the limit of a sequence of complex numbers.