R is the eighteenth letter of the Latin alphabet.

Semitic Rêš (the head) developed into Greek Ρω (Rô). The sound value /r/ however was maintained in Greek as well as Etruscan and Latin.

Romeo represents the letter R in the NATO phonetic alphabet.

R is also:

• In organic chemistry, the symbol for the hydrocarbon chain.
• In chemistry, the letter denoting the molar gas constant.
• A rating given for films given by the Motion Picture Association of America, see R (rating)
• The stock symbol for Ryder Systems Inc
• A statistical programming language; see R (programming language)
• The symbol used to represent the set of real numbers. Commonly displayed in the blackboard bold font.
• The variable R for electrical resistance
• The variable r for radius of a circle
• Symbol for roentgen
• In countries that recognize the British monarch as head of state, R stands for Rex (king) or Regina (queen) in court citations.

Two-letter combinations starting with R:

• ra rb rc rd re rf rg rh ri rj rk rl rm rn ro rp rq rr rs rt ru rv rw rx ry rz