Abstract: The Macau Science Satellite-1 (MSS-1) mission (https://mss.must.edu.mo/) is marked by a new high-precision constellation of satellites that will survey the Earth’s geomagnetic and space environment. MSS-1 consists of two satellites that are to be launched in the near future. Since these two low Earth orbit (LEO) satellites will operate in circular orbits, with an inclination of about 41°, they are expected to provide essential measurements covering the Earth’s lower-latitude regions—including, especially, the South Atlantic Anomaly (SAA). This special issue presents 18 articles to provide the international scientific community with details regarding the mission’s goals, relevant scientific research, on-board payloads, and international collaborations. Contributors are members of the scientific and engineering groups involved in the mission. In this preface, we categorize the articles and give some brief comments or editor’s recommendations.