Abstract: A typewriter keyboard arranged to take into account the frequency of occurrence of letters so that the keys for the most frequently occurring letters are positioned for easiest operation by the typist. Account is also taken of the frequency of occurrence of consecutive letters so that one finger or thumb will not have to operate different keys in rapid succession. The keyboard further includes keys to form letters or functional operations operable by the thumb. In one embodiment, two pluralities of keys are provided for operation by the fingers of the left and right hands, respectively, and two further pluralities of keys are provided for operation by the right and left thumbs, respectively.Each of the four pluralities of keys is arranged on a surface which is concave in two orthogonal directions.