Publisher Summary This chapter aims to provide a legal point of view for best execution policy, which is a universal concept of the duty of a firm to act in the best interests of its customers. Best execution is generally regarded as an extension of the long-standing legal principles of fiduciary duty and law of agency. Best execution is provided a legal basis in the United States through a concept known as “the shingle theory,” which states that by hanging out his shingle, a broker makes an implied representation to his customers that he will deal with them fairly and act in their best interest. Both the Newton and Geman cases addressed the issue of whether the execution of trades at the best displayed price constitutes best execution of better prices that may be reasonably available. Some have argued that the existence of the fiduciary duty under civil law renders unnecessary the use of regulatory standards of any kind. Legal matters are not restricted to the rights of the individual investor.