An object of the present invention is to provide an authentication system and method which can reduce a burden on a user while ensuring security by using a combination of a plurality of authentication methods. A method for authentication of the present invention comprises the steps of: obtaining a first authentication performance value for each transaction based on initial input information at a transaction; determining whether or not additional authentication is required for authentication of a person by comparing the first authentication performance value and the authentication performance threshold value required for authentication of a person; presenting, if the additional authentication is required, a plurality of authentication methods from which one authentication method or a combination of authentication methods can be selected so as to satisfy an additional authentication performance value obtained using the first authentication performance value and the authentication performance threshold value; and obtaining a second authentication performance value based on additional input information using the one or more authentication methods selected from the plurality of presented authentication methods, and determining whether to authenticate by comparing the additional authentication performance value and the second authentication performance value.