If early crewed outposts on Mars can develop adequate habitats and in-situ resource utilization capabilities, they may evolve into small permanent settlements. Their main aims would likely remain scientific exploration, as well as work required for the settlement to grow further and become (nearly) self-sustained. Even if the latter work is successful, a settlement will raise multiple practical, legal, and ethical questions which did not apply, or not to the same extent, to missions smaller in scale. For example, living conditions (tight living compartments, high levels of ionizing radiation, partial gravity, etc.) could cause new medical problems over the long term, and be risky for reproductive biology, thus endangering the viability of the community. If humans were to spend decades on Mars, a return to Earth may be hazardous. Finally, the identity of the settlement, and its relationship with terrestrial operators, founders, and legal systems, may be complex and should be considered well ahead of time.