Wood blocks date all the way back to the mid-700s in the Orient. They were the successor of stone rubbings, which involved carving calligraphy into a rock, inking the rock, then stamping paper with it. Wood blocks were more easily manipulable, could be made flatter and what was not wanted in the print could be carved away with a knife. Because of the uniform flatness of the surface of a wood block, multiple copies of a poster or public announcement could be made much faster and with more consistency than with a stone rubbing.
Wood type letterpresses arose in Europe in the 15th century with Johannes Gutenberg's development of reusable, movable type. If you have ever seen an original book from the 19th century or before, you have seen the distinctive look of a wood type letterpress. These letterpresses used blocks of a single letter, each set in a press to form words and then printed onto a page. When the printing was finished, the letter blocks could be removed and reset into an entirely new page to be printed. Over time, various metal materials were used to form the movable type. The metals lacked the aesthetically artistic feel of wood type, but held up much longer and could be worked at faster speeds.
In modern type, wood block is almost never used for printing letters because the letters on the wood block cannot be changed. After the planned printing is done, the block is no longer useful. Because of their unique look, though, wood blocks are often used by artists to produce prints. Many artists will carve a block to make a particular print, then number each print produced and destroy the block after the printing is finished. When you see a piece of art that has what looks like a large fractional number on it, such as 146/500, what it means is that piece was the 146th print of a total of 500 made before the printing medium was destroyed. This applies to all high-quality art prints, but is most frequently used with wood block prints.
Because it is so easily manipulable and creates a unique, rich looking inked page, wood type was used in letterpresses to print books. Old books that start each chapter with an intricately drawn and artistically detailed stylized first letter are made either from wood type or are a throwback to a technique that was common with wood type. Wood type gained currency as an artistic medium in the early 1800s when a process that allowed the mass production of wood block letters was developed, even though wood letterpresses had already been supplanted by various metal faced blocks of type. Letterpresses of all types have become a rarity, replaced first by linotype presses and then computer generated printing. Some specialty wood letterpresses remain, though, as an historic art form for specialty projects.