 Earth, as seen from space, is a beautiful sight. These amazing images of Earth are just one of the many benefits of space activities. Around 5,000 active satellites are currently orbiting Earth and providing tangible social, scientific, security, and economic benefits to billions of individuals all over the globe. This includes enhancing things that we rely upon on a daily basis such as cell phones, the internet, electronic banking, navigation, weather forecasting, communications, news, and entertainment. Indeed, space systems applications are now so intimately woven into the fabric of our modern information society that many people take the continuity of these space-derived data and services for granted. Yet the ability to continue to provide these important benefits from outer space is now threatened by a number of challenges. The Earth's orbital space environment is a finite resource and it's being used by an increasing number of space actors in potentially unsustainable ways. In the early days of the space age, the Earth's orbital environment posed only natural hazards to spacecraft operating there, such as space weather and impacts from meteoroids. However, in the decades that followed, more and more countries got involved in space and the environment has become much more congested. The number of satellites we're putting into space is increasing rapidly and there are also tens of thousands of defunct satellites and rocket bodies and other fragments that we collectively refer to as space debris. All of this poses an increasingly serious collision hazard to operational satellites and human spaceflight. There are currently about 28,000 pieces of human-generated debris in Earth orbit larger than 10 centimeters in size, each of which could destroy an active satellite in a collision. Statistical modeling indicates there are an estimated 700,000 pieces of orbital debris between 1 and 10 centimeters in size that are largely untracked. This existing orbital debris is largely concentrated in the same altitudes that are heavily used by satellites and in particular low Earth orbit and geostationary Earth orbit. These debris objects may also collide with each other, generating yet more debris. In 1978, NASA scientist Donald Kessler studied what would happen if such cascading debris growth continued unchecked. The Kessler syndrome predicts that there would be a critical point where the density of orbital debris would result in random collisions between debris objects. These random collisions would in turn generate more debris at a rate faster than it is naturally removed from orbit by the Earth's atmosphere. Although this process takes place relatively slowly over decades or centuries, we are already seeing it impose a cost on space activities. Satellites operating in congested regions have to manage a growing number of close-approach warnings and may need to expend precious fuel to avoid potential collisions with debris. As the amount of orbital debris grows, so do the risks of collisions, making some activities too unsafe, risky, or unprofitable to continue. In the early days of the space age, the financial and technological barriers to becoming a space actor were very high. Only a few countries had the wherewithal to build their own satellites. However, there are now many more affordable options for launching satellites into space. This is driving innovation of new space technologies and space applications at a pace never seen before. Together, these factors have led to an explosion of space activities all around the world. We are also seeing the emergence of space systems with hundreds and even thousands of satellites. These very large constellations of satellites hold out the promise of delivering low-cost space data and services to every corner of the globe on a continuous basis. But they also raise a number of questions about the safety of space operations and about equitable access to space for countries that are not yet at the point of building and operating their own satellites. One of the factors that has contributed to the proliferation of space debris and the high cost of space activities in the past is that rockets and satellites have traditionally been single-use systems. Unlike cars and planes, they don't get refueled or fixed when they break. However, we are starting to see the development of satellite servicing technologies that are paving the way for in-orbit activities such as refueling, repair, assembly, and manufacturing. These technologies could also be harnessed to remove the larger debris objects from space, thus reducing the risk of a cascade of debris collisions envisaged in the Kessler syndrome. These technological capabilities will be foundational for a future space economy with the potential to benefit billions of people on Earth. Such a space economy will only be sustainable if we balance the opportunities and needs of the present users of space with the need to preserve the space environment for future generations. Space sustainability is addressing these challenges to ensure that the space environment remains suitable for exploration and use by the current and future generations of all countries. Such is the growing international concern about space sustainability that in 2019, the United Nations Committee on the Peaceful Uses of Outer Space adopted a set of 21 guidelines for the long-term sustainability of outer space activities. In the preamble to these guidelines, space sustainability is defined as the ability to maintain the conduct of space activities indefinitely into the future in a manner that realizes the objectives of equitable access to the benefits of the exploration and use of outer space for peaceful purposes in order to meet the needs of the present generations while preserving the outer space environment for future generations. Meeting the challenges of space sustainability requires coordinated action at a global level from governments, industry and civil society. It requires that we implement regulatory measures and other incentives to promote responsible behaviors in outer space, informed by principles similar to those that we already use to promote environmentally and socially responsible investment and development on Earth. In short, ensuring the sustainability of activities up there in space is foundational to ensuring our economic prosperity, peace and sustainable development down here on Earth. The Secure World Foundation works with governments, industry, international organizations and civil society to develop and promote ideas and actions to achieve the secure, sustainable and peaceful uses of outer space that will benefit Earth and all its peoples. To find out more, visit SWfound.org.