The International Union of Crystallography (IUCr) is a professional association that promotes international cooperation in crystallography and related fields. It was founded in 1948 and has played a crucial role in advancing the study and application of crystallography. The IUCr is governed by an elected body of officials, including a president who serves a term of four years. The list of presidents includes notable scientists in the field of crystallography and reflects the pioneering work and leadership that have shaped the discipline.