One of the directions of the plan is to promote the implementation of behavioural strategies to reduce risks associated with heat waves. [...] The goal of the evaluation was to estimate the rate of penetration of prevention messages among Montrealers aged 65 and over, to assess the messages’ impact on knowledge and behaviours adopted during heat waves, and to explore the factors influencing behavioural response. [...] The objective of the campaign is to inform the general public, especially the most vulnerable individuals, of the measures to take to avoid health problems associated with heat waves. [...] There are three components to the evaluation: The first assesses the dissemination of the messages among the general population. [...] Nonetheless, to foster acquisition of new knowledge— to say nothing of changes in behaviours—messages should be developed based on a deep understanding of the target audience to tailor the campaign goals, determine the choice of the communication channel (by selecting the information sources most commonly used by the targeted population to increase exposure), and define the contents and style of t