This chapter provides a foundational exploration of Earth as a complex and dynamic system within the broader context of the solar system. This chapter introduces the fundamental concepts of physical geography, including Earth’s shape, dimensions, and the geographic grid system. It examines Earth’s relationship with the Sun, which drives its energy systems, seasons, and climate. The origins and evolution of Earth’s atmosphere, oceans, and biosphere are discussed to illustrate the intricate interactions among the Earth’s spheres. Key topics include the Earth’s geophysical characteristics, the geographic grid’s importance, and the atmosphere’s integral role in Earth’s (bio)geochemical and climate systems. This chapter emphasizes the critical need for Earth system science (ESS) to understand and manage the environmental challenges posed by climate change, natural hazards, and anthropogenic impacts. This introduction sets the stage for exploring Earth’s interconnected systems and their influence on life and planetary sustainability.