This book deals specifically with the use of insider information in the capital market, conduct carried out by those with powers and confidential information due to their position within publicly traded companies. In today's economic and business scenario, joint-stock companies have emerged as the form of company best suited to large enterprises. As a result, there is also a growing need to guarantee greater security for those who choose them as an investment option. With this in mind, the book introduces the basics of business companies, with a greater focus on public limited companies, including management bodies, standards of conduct and the duties of directors, as a way of preventing this practice. Finally, it elucidates the conduct of insiders and the practice of insider trading, demonstrating its harmfulness to the capital market, as well as the need for prevention and repression, through civil, administrative and criminal liability.