α-Helix is a secondary structure of proteins formed by twisting of polypeptide chain into right handed screw like structures. Which type of interactions are responsible for making the a-helix structure stable?

A stable α-Helix is formed as a right handed screw helix structure as the –NH group of each amino acid residue hydrogen is bonded to the –C=O of an adjacent turn of the helix.

Structure of stable α-Helix. Image from Wikipedia using Wikipedia Commons License.