The article considers the different options available to international tribunals, especially the International Court of Justice, when facing cases that raise scientific and technical issues. While international tribunals can sometimes leave it to the parties to seek an agreement on such issues or resort to legal reasoning to avoid making technical and scientific assessments, other methods may need to be adopted. The Court can rely on the expertise provided by the parties, informally consult “invisible” experts – as long as their views are not likely to affect the content of the decision – or proceed to the appointment of experts or assessors, the latter participating in the deliberations without the right to vote. Due process implies that the parties should be able to comment on the views expressed by Court-appointed experts. This requirement may create difficulties for the Court in reaching a decision on scientific or technical issues.