IAAO Acronyms The International Association of Assessing Officers is a nonprofit, educational and research association. It is a professional membership organization of government assessment officials and others interested in the administration of the property tax. The IAAO was founded in 1934, and now has a membership of more than 7, 300 members worldwide from governmental, business, and academic communities. IAAO members subscribe to a Code of Ethics and Standards of Professional Conduct and to the Uniform Standards of Professional Appraisal Practice. The mission of IAAO is to promote innovation and excellence in property appraisal, assessment administration, and property tax policy through professional development, education, research, and technical assistance. IAAO will be the internationally recognized leader and preeminent source for innovation, education and research in property appraisal, assessment administration and property tax policy.