Step 1: Use the trigonometric identity.
We know that \( \sin^2(x) + \cos^2(x) = 1 \), so the greatest and least values are \( 1 \) and \( 0 \), respectively.
Step 2: Conclusion.
The greatest value is 1 and the least value is 0.
Final Answer:
\[
\boxed{1 \text{ and } 0}
\]