Fundamental may 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 simple or "fundamental" ideas based on faith in a system of thought
• Fundamentals: Ten Keys to Reality, a 2021 popular science book by Frank Wilczek
• The Fundamentals, a set of books important to Christian fundamentalism
• Any of a number of fundamental theorems identified in mathematics, such as:
  • Fundamental theorem of algebra, a theorem regarding the factorization of polynomials
  • Fundamental theorem of arithmetic, a theorem regarding prime factorization
• Fundamental analysis, the process of reviewing and analyzing a company's financial statements to make better economic decisions