We, as humans, are natural taxonomists, with a preference for classifying things as a means of understanding them. Taxonomy (the classification of all organisms) is central to our understanding of biodiversity and evolution, and, therefore, to our ability to conserve organisms and ecosystems. However, the way scientists classify organisms has changed over time as a series of new technological innovations have arisen, mainly focused on new ways of visualizing comparisons. These innovations, and the impact they have had on how we ‘see’, are the focus of this chapter. First, we explore how Aristotle and Carl Linnaeus helped found taxonomy by developing schemes to classify organisms based on similarities and differences in their gross (macroscopic) anatomy. While many of these classifications are still accepted to this day, others have been refined as new lines of evidence arose. The invention of microscopy and the several types of visualizations associated with it e.g. photomicrographs, allowed later scientists to start classifying smaller organisms and develop their understanding of the fundamental biology of large ones. Finally, the late twentieth-century emphasis on visualizing genes and not anatomy, has also driven significant reclassifications. Broadly speaking, anatomical based definitions of taxonomy are better at showing ecological patterns, while genetic definitions help us to recognize underlying similarities between species that may look very different, or conversely to see that similar-looking animals are in fact completely distinct species that happen to have arrived at a similar body plan. Fundamentally, the way we do taxonomy, i.e. looking for similarities or differences, has remained the same, but integrating new visualizations into classifications has both clarified how organisms are related in terms of evolution, and progressed biological science as a whole.