算术（arithmetics）是数学最古老且最简单的一个分支，几乎被每个人使用着，从日常生活上简单的算数到高深的科学及工商业计算都会用到。一般而言，算术这一词指的是记录数字某些运算基本性质的数学分支。常用的运算有加法、减法、乘法、除法，有时候，更复杂的运算如指数和平方根，也包括在算术运算的范畴内。算术运算要按照特定规则来进行。

自然数、整数、有理数（以分数的形式）和实数（以十进制指数的形式）的运算主要是在小学和中学的时候学习。用百分比形式进行运算也主要是在这个时候学习。然而，在成人中，很多人使用计算器，计算机或者算盘来进行数学计算。

Arithmetic or arithmetics (from the Greek ἀριθμός arithmos, "number") is the oldest and most elementary branch of mathematics. It consists of the study of numbers, especially the properties of the traditional operations between them—addition, subtraction, multiplication and division. Arithmetic is an elementary part of number theory, and number theory is considered to be one of the top-level divisions of modern mathematics, along with algebra, geometry, and analysis. The terms arithmetic and higher arithmetic were used until the beginning of the 20th century as synonyms for number theory and are sometimes still used to refer to a wider part of number theory.