We have chosen a dozen of Spinoza's letters covering a wide variety of topics and correspondents. Spinoza's correspondece gives us an insight into his more personal circumstances, and even opinions on matters not normally covered in his philosophical treatises. The philosopher from The Hague would write in a very familiar way, very different from the usual philosophical tone of his most renowned works. Among the people that maintained corresponde with Spinoza, we have to remark Gottfried Leibniz, a great man of science, writing to Baruch Spinoza on a very technical matter, lens craft. Lens crafting was the actual profession of Spinoza, and he was known in Europe as one of the finest in his craft. Some other letters give us insight into math...