At the beginning of the 20th century, it was admitted that our atmosphere could not extend beyond a few tens of kilometres. Shortly after the midst of that same century, it was understood that the Earth is surrounded by a complex and rich plasma environment, conditioned by solar activity, extending over several tens of thousands of kilometres. Today, we know that our planet’s boundaries extend all the way to the Sun. This book tells the long story of humanity’s efforts to understand the boundaries of the Earth and its influence from the external celestial objects dominated by our closest star, the Sun. It also reveals the impact that solar activity is having on our technological societies, from the most beautiful to the most fearsome: Polar auroras and northern tourism, power and communications cuts, GNSS positioning degradations, planes losing contact with control towers, astronauts under threat, space... It presents, in a clear and educational way, this new and exciting discipline: space weather and space climate, its physics, its instruments, its methods, from modelling to artificial intelligence, its forecasting centres.