Objectives: To assess the level of consensus amongst an international panel of public health nutrition leaders regarding the essential competencies required for effective public health nutrition practice. Design: A modified Delphi study involving three rounds of questionnaires. Subjects: A panel of 20 public health nutrition experts from seven countries in the European Union, the USA and Australia. Results: Expert panellists completed three rounds of the study relating to competencies. A literature review conducted as a prelude to the expert panel survey identified common competency units from the fields of public health, health promotion, nutrition and dietetics, and health education. These were categorised into seven competency areas including analytical, socio-cultural and political, public health service, communication, management and leadership, nutrition science and professional competency categories. There was strong initial agreement ($90% of panellists at Round 1) that developing internationally recognised competencies for public health nutrition specialists was a priority. Twenty-six of an initial listing of 52 competency units were rated as essential competencies by $80% of the panellists after Round 1. Iteration rounds resulted in the addition of five extra competency units suggested by panellists after Round 1 and an increase by 13 in the number of competencies rated as essential to consensus levels. From a total of 57 competency units rated after the final survey round, 41 competency units were rated as essential competencies by $80% of the panellists (consensus), with 21 of these unanimously rated as essential competencies. Conclusions: There is strong international agreement amongst public health nutrition leaders in Europe, the USA and Australia about a range of competencies required for effective public health nutrition practice. Essential competency units identified can be used to develop and review competency standards for public health nutrition.