Knowledge-based authentication (KBA) is provided using historically-aware questionnaires. The KBA can obtain a plurality of historically different answers from the user to at least one question; challenge the user with the question for a given period of time; receive a response from the user to the question; and grant access to the restricted resource if the response is accurate for the given period of time based on the historically different answers. Alternatively, the KBA can be based on historically aware answers to a set of inter-related questions. The user is challenged with the inter-related questions for a given period of time. Historically different answers can comprise answers with applicable dates, or correct answers to the question over time. Historically aware answers can comprise an answer that is accurate for an indicated date or period of time. An accurate response demonstrates knowledge of multiple related personal events.