Intrusion detection system (IDS) is an application system monitoring the network for malicious or intrusive activity. In these systems, malicious or intrusive activities intrusion can be detected by using information like port scanning and detecting unusual traffic, and then they can be reported to the network. Since intrusion detection systems do not involve predefined detection power and intrusion detection, they require being intelligent. In this case, systems have the capability of learning. They can analyze packages entering the network, and detect normal and unusual users. The common intelligent methods are neural networks, fuzzy logic, data mining techniques, and genetic algorithms. In this research, the purpose is to study various intelligent methods.