The square root of 36 is \( \sqrt{36} = 6 \). The number 6 is an integer, and all integers are rational numbers.
A rational number is defined as a number that can be expressed as the quotient of two integers (where the denominator is not zero). Since 6 can be expressed as \( \frac{6}{1} \), it is a rational number.
Therefore, \( \sqrt{36} \) is rational.