How Young Ganesh got it's Elephant Head

Once upon a time, the Goddess Gauri (consort of Lord Shiva), while bathing, created Ganesha as a pure white being out of the mud of Her Body and placed Him at the entrance of the house. She told Him not to allow anyone to enter while she went inside for a bath. Lord Shiva Himself was returning home quite thirsty and was stopped by Ganesha at the gate. Shiva became angry and cut off Ganesha's head as He thought Ganesha was an outsider.

When Gauri came to know of this she was really mad. To console her grief, Shiva ordered His servants to cut off and bring to Him the head of any creature that might be sleeping with its head facing north. The servants went on their mission and found only an elephant in that position. The sacrifice was thus made and the elephant's head was brought before Shiva. The Lord then joined the elephant's head onto the body of Ganesha.

Lord Shiva made His son worthy of worship at the beginning of all undertakings, marriages, expeditions, studies, etc. He ordained that the annual worship of Ganesha should take place on the 4th day of the bright half of Bhadrap