Definition
The Necessary and Proper Clause, sometimes called the Elastic Clause, is the final paragraph of Article I, Section 8. It authorizes Congress to make all laws necessary and proper for carrying out its enumerated powers and the other powers vested in the federal government.
The clause does not grant a new freestanding power. Instead it confirms that Congress may choose reasonable means to put its listed powers into practice.
Why it matters
How it works
When Congress relies on the clause, a law must be tied to a legitimate enumerated end and must be a reasonable means toward that end. The classic interpretation reads necessary as appropriate or convenient rather than absolutely indispensable.
A narrower view would require a tighter fit between the means and the granted power. The word proper adds a further limit, signaling that even useful measures must not violate other constitutional principles such as state sovereignty.