What is the most important biological process that occurs on Earth? You might immediately think of all organisms have to respire in order to release energy. But all complex organisms require oxygen to respire and where does the oxygen come from? After all, as far as we know we are the only planet in the solar system with elemental oxygen in our atmosphere. The answer is that all the oxygen on Earth is made by the process of photosynthesis; performed by plants and blue-green algae. Life would not exist on this planet as we know it; without photosynthesis. In addition, all the carbon-based organic molecules that organisms are made of; such as carbohydrates; proteins and fats; originate from photosynthesis. So that is what this book is photosynthesis. I explain all the most important principles and facts and put them in context; on top of giving answers to common exam questions that you might face. I hope you enjoy this book and gain insight into the process of photosynthesis and that it inspires you to further understand and appreciate biology in general.