The first big microscopy advances came in 1665, when Robert Hooke published the Micrographia, a collection of copper-plate illustrations of objects he had observed with his own compound microscope. He coined the term 'cell' when looking at a piece of cork under 30x magnification.
In the late 1660s, Antony van Leeuwenhoek began to grind his own lenses and make simple microscopes. Each microscope was really a powerful magnifying glass rather than a compound microscope. Leeuwenhoek's hand-ground lenses could magnify an object up to 200 times! He observed animal and plant tissue, sperm cells and blood cells, minerals, fossils, and much more. He also discovered nematodes and rotifers (microscopic animals), and he discovered bacteria while looking at samples of plaque from his own and others' teeth.
1900s till now: In 1931, a pair of German scientists invented the electron microscope. This kind of microscope directs a beam of speeded-up electrons at a cell sample; as the electrons are absorbed or scattered by different parts of the cell, they form an image that can be captured by an electron-sensitive photo plate. This model enables scientists to view extremely small parts, magnified as much as one million times. (Check out these electron microscope images to see what it looks like.) The only drawback is that living cells can't be observed with electron microscopes. However, compound microscopes are being improved with digital and other new technology, making microscopy better for everyone from kids to lab microbiologists.