Woodworkers use joints to provide structural reinforcement to their work, as well as to add an element of beauty. Modern glues can be quite strong, and used to chemically bond the long grain of two or more pieces of wood together. Some joints, such as wedged tenon, are so strong that they do not require any glue, although glue helps to make them permanent. Other joints, such as the box or finger joint, combine both mechanical and glue strength to create a permanent bond.
There are literally thousands of different woodworking joints, and I use a wide variety of them in my work. The most common joints are the mortise & tenon, the lap or half lap, the box joint, the dado, and the dovetail. On this recent piece I used a Japanese joint called the "nejiri arigata," or twisted dovetail. If you look closely, you'll realize there's no obvious way for these two pieces of wood to go together (they slide in at a 45-degree angle). As a result this joint is incredibly strong, and will never come apart.
The Japanese are justifiably famous for the many intricate joints they've created over the centuries. The complexity of their joinery stems from the need to create strong work without the use of glue or metal fasteners, neither of which was available to the ancient Japanese. Although modern construction techniques and materials have obviated the need for such complexity, craftsmen today still enjoy incorporating complex joints into their work for a variety of reasons: the reliance on traditional methods, the beauty of such joints, and as a virtuoso display of skill.
The dovetail has long been considered the hallmark of fine furniture and craftsmanship, though not all of my work calls for this joint. It is so-named because of its characteristic shape -- it looks like the tail of a bird. It's an extremely strong joint, generally used to join two orthogonal surfaces, such as the side and top of a cabinet. You can usually find dovetails on the outsides of drawer boxes in well made contemporary cabinetry.