Space is a key geographical concept. Along with other core concepts such as place, landscape, scale, mobility, nature, and environment, it helps define the discipline as one that is explicitly spatial in its focus and thinking. Unsurprisingly then, geography is often described as a spatial science. As such, while human geographers are interested in social, political, cultural, economic, and environmental issues and undertake historical analyses, they do so cognizant of the role of space in shaping the world around us and using theories and methods that illustrate why space and spatial processes matter. This article details how thinking about space has evolved significantly since the 1950s, focusing in particular on how theorists have conceptualized the ontology of space. To illustrate the differences between the various ways of thinking about space, an example of how cities are understood within different ontological frameworks is used.