Abstract: Voice Over Internet Protocol (VOIP) has gained tremendous attention due to the growing use of the internet. There are many protocols that can be used to achieve the transmission of voice over the Internet Protocol (IP). This thesis covers the issue related to study the characteristics belong to four of the most important VOIP Protocols (Session Initiation Protocol, H.323 Protocol, Media Gateway Control Protocol, H.248/Megaco Protocol) which used to set up and tear down voice communication, carry information required to locate users and negotiate capabilities, and a table accomplished from this study for the comparison purpose between the four VOIP protocols. Also the thesis covers the issue belongs to implementing a VOIP system using the H.323 protocol which is one of the most important VOIP protocols for its versatility to provide real-time voice communication over a common Local Area Network (LAN) infrastructure. VOIP system using the H.323 protocol was built depending on the functionality of Visual CSharp.NET programming language and was tested on a LAN network with 2 PCs. The implemented program enables the users to make a conversation by voice as well as by text and also enables the sharing of the images. The system was satisfactory from the point of voice quality, enabling various types of expedients communication (voice call, text, sharing images), and the ability which introduced to the user to communicate with two different users using two different types of expedients at the same time by entering the two IP addresses related to the two users.