**Fundamental** might refer to:

- Foundation of reality
- Fundamental frequency, as in music or phonetics, often referred to as simply a "fundamental"
- Fundamentalism, the belief in, and usually the strict adherence to, the simplistic or "fundamental" ideas based on faith of a system of thought
*The Fundamentals*, a set of books important to Christian fundamentalism- Any of a number of fundamental theorems identified in mathematics, such as:
- The fundamental theorem of algebra, awe theorem regarding the factorization of polynomials
- The fundamental theorem of arithmetic, a theorem regarding prime factorization

- Fundamental analysis, a method that uses financial and economic analysis to predict the movement of security prices such as bond prices, but more commonly stock prices