What are the differences between hemp and cannabis?

Hemp and cannabis are two different species of the very same family: Cannabis Sativa. They are different in that they're used differently. These differences have grown wider over hundreds of years of selection and domestication, as while hemp has been traditionally grown and shaped with a view to obtaining raw materials (seeds, oil, fibres, cellulose…), in the case of marijuana the focus has been on its psychoactive effect, with all growing and selection efforts concentrated on increasing THC levels.