A modern concert pedal harp usually has seven pedals.
The seven pedals correspond to the seven note names in the diatonic scale: C, D, E, F, G, A, and B. Each pedal normally has three positions, allowing the player to set the associated notes as flat, natural, or sharp across the harp’s range.
This mechanism lets a concert harp perform in many keys while retaining the instrument’s open-string resonance. The pedals are arranged in two groups, with three on the left and four on the right, so the player can operate them with both feet.
A concert pedal harp commonly has 47 strings, but the number of strings and the number of pedals are different facts. Smaller lever harps may use levers at individual strings instead of pedals, so not every harp has seven pedals.