The evolution of prohibition of insider trading in the United States has marked its regulation worldwide. Different systems of insider trading regulation have emerged from the theories set by American courts. The systems nowadays are not compatible and seem to protect different sets of values based on the logic behind the regulations. Most of the world systems have adopted the Equal access theory approach, while the United States bases its system on fiduciary duty. Inside the theories, different sets of rules and tests were developed in order to help establish whether an act qualifies as insider trading. However, even though the same tests are used worldwide, they are used and interpreted in different ways, which leads to even bigger differences in regulation. This Thesis focuses on the differences between four big systems, comparing the theories they have developed from, and the values they intend to protect.