The Mars Society is a nonprofit organization that advocates for human exploration and colonization of Mars. It was founded by Robert Zubrin in 1998 and its principles are based on Zubrin's Mars Direct philosophy, which aims to make human missions to Mars as feasible as possible. The Mars Society generates interest in the Mars program by garnering support from the public and through lobbying. Many current and former Mars Society members are influential in the wider spaceflight community, such as Buzz Aldrin and Elon Musk.

Since its founding, the Mars Society has organized events and research activities. It has hosted its annual International Mars Society Convention and operated research projects such as the Flashline Mars Arctic Research Station and the Mars Desert Research Station, both using Mars analog habitats. Both of the stations are placed in remote locations for research. Crew members perform simulated extravehicular activities, carry out research assignments and reside at the station on strictly rationed supplies. The organization also hosts a college robotics competition in Utah called the University Rover Challenge.

The Mars Society is a 501(c)(3) nonprofit organization that is funded by donations and operated by volunteers. Membership to the Mars Society is available to all on payment of a small fee. The society's aims are garnering public support for human Mars missions, lobbying government and space agencies, and verifying mission proposals via Mars analog habitats. These goals were set out in the Founding Declaration of the Mars Society.

The Mars Society's founder and current president is Robert Zubrin. Notable current and former members of the organization include Buzz Aldrin, Elon Musk, Gregory Benford and James Cameron. The society is a member of the Alliance for Space Development and has chapters in Australia, Canada, Europe, Japan, and many other countries. Since its foundation in 1998, the society organizes the annual International Mars Society Convention, with presentations primarily about Mars exploration and colonization.

In the 2019 filing to the Internal Revenue Service, the Mars Society reported to receive around US$400,000 in donations per year. Some noteworthy expenses include the annual Mars Society convention (US$58,800), the Mars Desert Research Station (US$200,000), and the University Rover Challenge (US$46,500). The Mars Society's Taxpayer Identification Number is 31-1585646.

Many of the Mars Society's members believe that a human mission to Mars is achievable within a decade (as laid out in Zubrin's Mars Direct) and such a mission would lay the foundation for the colonization of Mars. The Mars Direct philosophy has permeated through the society's lobbying efforts. During testimony to the 2009 Augustine Commission, a panel set up by the Obama administration to outline the future of the U.S. space program, Zubrin advocated initiating a lean human Mars program in a similar manner to Mars Direct. The committee was indifferent to the testimony; in the final report, the commission concluded that a human Mars mission in general would "demand decades of investment and carry considerable safety risk to humans".

In 2005, Robert Markley, a science fiction researcher, pointed out that Zubrin used his president of the Mars Society position to espouse his own views on how human missions to Mars should be carried out. To make the Mars Direct plan appealing to the American public, he compared Mars to the Great American Frontier and the colonization of Mars as a way to resolve social stagnation and "Hobbesian despair" on Earth. Mars would be a way to give birth to an ideal society. In effect, Markley commented, Zubrin has created an "interplanetary vision of manifest destiny". Most members of the Mars Society agreed with the less extreme version of Zubrin's ideal, in that colonizing Mars is critical for preventing a dystopian future for humankind.

Oliver Morton commented in 2003 that the Mars Society is a fundamentally "utopian and escapist organization". He observed that many Mars Society convention participants were unhappy with government space programs. As a consequence, they favored funding alternatives that are often impractical, such as sponsorship deals, private philanthropy, and Martian bonds (on the basis of future resources and profits). Markley commented in 2005 that the Mars Society is somewhat similar to the Royal Society at its founding in the 17th century: "as much of a social club of enthusiasts as a professional scientific organization", with influences from science fiction. In a way, he continued, the Mars Direct plan provided a grand vision for future Martian endeavors to follow and the Mars Society is a platform for exploring the implications of Mars colonization.