Disclosed are a washing machine and a controlling method, capable of maintaining an optimal temperature for efficient generation of foam to perform foam washing that uses a large amount of foam in washing laundry, thereby accomplishing optimal washing efficiency. The controlling method for the washing machine according to the present invention comprises supplying washing water with detergent required to generate foam, generating foam using detergent water which is a mixture of the washing water and the detergent, transmitting heat to the generated foam by heating the detergent water, and washing laundry using the foam.