This paper offers a brief overview of the law and economics debate over the need to regulate insider trading. It summarizes various agency, market, and contractual (or „Coasian”) theories of insider trading propounded over the course of this longstanding debate. Agency theories analyse the effects of insider trading on the manager-shareholder relationship. Market theories analyse the overall market efficiency of insider trading, including its impact on stock prices accuracy and stock market liquidity. According to the outcome of these analyses, the parties to the debate are divided into proponents of insider trading regulation and advocates of a deregulated insider trading activity. A distinct group of scholars opts for a private regulation of insider trading activity, which is regulation at the level of the firm through the means of a contract concluded between interested parties, instead of state regulation.