The Institute of Directors (IoD) is a British professional organisation for company directors, senior business leaders and entrepreneurs. It is the UK's longest running organisation for professional leaders, having been founded in 1903 and incorporated by Royal Charter in 1906. The Royal Charter charged the IoD with promoting free enterprise, lobbying government and setting standards for corporate governance.

The IoD is located in a Grade I listed building at 116 Pall Mall in London, formerly the United Service Club. Members of the IoD also gain access to co-working spaces around the UK, bespoke market intelligence, tailored tax and legal support, exclusive member-only events along with discounts on IoD professional development courses and events.

From a high of 55,000 members in 2005, the IoD currently has just over 20,000 full members, with membership stabilising year on year. Members of the IoD come from companies of all sizes and from all industries. Around 70% are self-employed or work for small and medium-sized enterprises, while 78% of FTSE 100 companies have an IoD member on their board or in a senior management position.