The Mars Society is not a single organization but an association of independent national branches, operated as non-profit organizations of volunteers according to national laws.

In Europe each country organizes and operates its own specific Mars Society chapter and defines its own specific focus and projects in accordance with the common Mars Society goals.

The different countries with Mars Society branches are represented in a so-called Mars Society Steering Committee, which convenes normally once a year for discussing common matters and eventually agreeing on common goals and undertakings, as appropriate.

The Mars Society organises each year conferences in the US and Europe, which attract a wide variety of scientists and Mars enthusiasts.