The letterpress printing technique was invented in 1447/1448 and it is inherently connected with the name of Johann Gutenberg. He improved typesetting by using serial cast types. Letterpress belongs to relief printing techniques that had been known for many centuries before Johann Gutenberg. It is presumed that the relief printing appeared first in China in the 9th century. However, printing was very slow, expensive, inefficient, and thus little used. It experienced a boom after Gutenberg's innovation.
Johann Gutenberg introduced several improvements. First, he invented typefoundry. It enabled serial production of types with identical shapes. As the first step, a calligraphic artist prepared an original die (so called patrix) which was a mirror image of the letter. This was used as a stamping die. A matrix (forme) was produced by imprinting the die into a softer metal. A melted metal was poured in the matrix to create a type, i.e. a reversed image of the letter. Types were casted from a type metal. It was an alloy of tin, lead, and antimony. Also this was probably a Gutenberg's invention. This alloy was highly wear-resistant and the types were not rapidly distorted.
The types could be easily aligned in uniform typesettings thanks to identical shapes and heights. It means that the printing forme could be assembled for a complete quire. This was indeed a great progress since till then the individual types were printed separately. Furthermore, the text was accurately aligned and the spaces were identical.
Printing itself was performed so that a complete typesetting was composed first. Then it was coated by a black printing ink using leather pads and the composition was printed on the paper. Naturally, the pressure was required for printing. Printing took place in the binding press. Binding press was another Gutenberg's invention - in principle it was just a modified wine press. This letterpress method had been used without significant modifications until the end of 18th century.
Nowadays, photopolymer plates are used for letterpress, and binding presses are fully automated. Otherwise the principle stays all the same. However, the letterpress is no more used for standard printing but it was replaced by offset printing. Primarily it was due to costs of letterpress. Also the speed of binding machines does not reflect today's requirements. Nowadays the letterpress is used almost solely for special purposes, e.g. impression or blind blocking (blind stamping).