Telegraph key is a general term for any switching device used primarily to send Morse code. Similar keys are used for all forms of manual telegraphy, such as in electrical telegraph and radio telegraphy.

Since its original inception, the telegraph key's design has developed such that there are now multiple types of keys.

A straight key is the common telegraph key as seen in various movies. It is a simple bar with a knob on top and a contact underneath. When the bar is depressed against spring tension, it forms a circuit and allows electricity to flow. Traditionally, American telegraph keys had flat topped knobs and narrow bars (frequently curved.) British telegraph keys had ball shaped knobs and thick bars. This appears to be purely a matter of culture and training, but the users of each are tremendously partisan. Straight keys have been made in numerous variations for over 150 years and in numerous countries. They are the subject of an avid community of key collectors. Straight keys used by telegraph operators also had a "shorting bar" that closed the electrical circuit when the operator was not actively sending messages. This was to complete the electrical path to the next station so that the sounder would operate, as in the operator receiving a message from the next town. The shorting bar is not necessary in amateur radio use except as an aid to help tune the transmitter.