Understanding and combatting biodiversity loss are critical tasks facing our planet. They are made especially difficult because much of the earth’s biodiversity is concentrated in abundant and speciesrich groups of invertebrates like insects. Traditionally, samples of insects have been analyzed manually by experts using morphology. Not only does this necessitate taxonomic expertise, but it is also error-prone, time-consuming, and often involves commercial microscopes that are too expensive for many countries in the Global South where most species are found. The alternative to expert sorting with morphology is the use of DNA barcoding. However, this requires a well-equipped laboratory and an entirely different skill set. We present an alternative solution: a low-cost, open-source photomicroscope for taking high-resolution, focus-stacked images that can be used for insect classification: the Entomoscope. We describe two different versions of the Entomoscope, a standalone version that can be operated without additional hardware and an even simpler Version, that requires a computer. We show that the optics are of sufficiently high quality to classify specimens with >95% accuracy into 15 different types of insects (mostly ’families’ according to the Linnean classification). The classifier can be successively extended or individually trained for specific classification tasks. Here, we provide building instructions, 3D files, and a list of commercially available parts so that everyone can build their own Entomoscope. Open-source DIY hardware like the Entomoscope facilitates affordable, cutting-edge biodiversity research by entomologists around the globe.