Many firms keep pay secret. They do not make information about what their employees are paid available inside or outside of the firm, i.e. to other employees or to the public at large. Indeed, many firms discourage their employees from, or sanction them for, disclosing their pay. Against this, I argue that there are good moral reasons for firms to be transparent about pay. Pay transparency prevents injustice, promotes autonomy, and increases efficiency. After presenting the positive case for pay transparency, I defend it against objections, including the most common reasons firms give for keeping pay secret.