Distributed Denial of Service (DDoS) attack is a coordinated effort between several machines to attack one or multiple target systems. Indeed, the attack is through imposing additional burden on system resources or flood computation and communication resources, the server services for legitimate users, are unavailable. In general, if we have categorized security into three areas of confidentiality, integrity and availability, distributed denial of service attacks threaten a third option. Since the distributed denial of service attacks caused by improper operation of information system and its users from accessing the services excluded and also to maintain vital system resources, such attacks are detected immediately. Hence, in this paper, we investigate such attacks and some of their detection mechanisms. In this paper, initially introduced such attacks, then are presented the various categories of these attacks, afterwards, several methods have been proposed to detect distributed denial of service attacks. Finally, these methods are compared and the advantages and disadvantages of them are briefly mentioned.