The National Academy of Sciences is made up of two class members: fellows and foreign members. The class of fellows is made up of 40 members and a variable number of members in excess, both with the same rights and duties. The number of fellows in excess is determined by, and equal to, the number of fellows that have reached 70 years of age and are members for at least 5 years.

The class of foreign members is made up of 25 members.

The assembly meeting takes place twice a year in the spring and in the fall.