Article about the Canada’s National Advisory Committee on Immunization (NACI), from Vaccine, Volume 28, Supplement 1, 19 April 2010, A58–A63. The National Advisory Committee on Immunization (NACI) provides medical, scientific, and public health advice on the use of vaccines in Canada. This article describes the structure and processes of NACI, as well as its approach to evidence-based decision-making. In a rapidly evolving and complex immunization environment, NACI has faced challenges in its endeavour to make thorough and timely evidence-based recommendations. Making population-level recommendations without formally considering the full spectrum of public health science (e.g. cost-effectiveness) presents difficulties in the implementation of NACI's recommendations. Although an improved and more transparent evidence-based NACI decision-making process is now in place, this is continuing to evolve with a current review of structures and processes underway to further improve effectiveness and efficiencies.