|Founded||Santa Clara, California (1997)|
|Headquarters||San Jose, California, U.S.|
|Michel K. Susai, Founder & CEO|
Citrix ADC is a line of networking products owned by Citrix Systems. The products consist of Citrix ADC, an application delivery controller (ADC), NetScaler AppFirewall, an application firewall, NetScaler Unified Gateway, NetScaler Management & Analytics System, and NetScaler SD-WAN, which provides software-defined wide-area networking management. NetScaler was initially developed in 1997 by Michel K Susai and acquired by Citrix in 2005. Citrix consolidated all of its networking products under the NetScaler brand in 2016. 
The NetScaler line of products are part of Citrix Systems' networking business. It includes NetScaler ADCs, NetScaler Unified Gateway, NetScaler AppFirewall, NetScaler SD-WAN, and NetScaler Management & Analytics System. The products can work in conjunction with other Citrix offerings, including its Xen line of products.
Citrix ADC is Citrix Systems' core networking product. It is an application delivery controller (ADC), a tool that improves the delivery speed and quality of applications to an end user. The product is aimed at business customers and it performs tasks such as traffic optimization, L4-L7 load balancing, and web app acceleration while maintaining data security.
Citrix ADC monitors server health and allocates network and application traffic to additional servers for efficient use of resources. It also performs several kinds of caching and compression. It can be made a server proxy, process SSL requests, and offers VPN and micro-app VPN operations. It also includes NetScaler application firewall and SSL encryption capabilities. NetScaler ADC can manage traffic during DDoS attacks, making sure traffic gets to critical applications. Additionally, Netscaler's logs of network activity feed into Citrix's cloud-based analytics service and are used to analyze and identify security risks.
There are four versions of Citrix ADC: NetScaler MPX, a hardware-based appliance for use in data centers; NetScaler SDX, a hardware-based appliance intended for service providers that provides virtualization delivering multitenancy for virtual and cloud-based data centers; NetScaler VPX, a software-based application that is implemented as a virtual machine and intended for small business use; and NetScaler CPX, a NetScaler ADC packaged in a container and designed for cloud and microservices applications.
In addition, the NetScaler line of products include Citrix SD-WAN, formerly CloudBridge SD-WAN, which provides software-defined wide-area networking and branch networking. NetScaler Unified Gateway offers secure remote access of virtual desktops and a variety applications from a single point of entry and with single sign-on (SSO).
The NetScaler Management and Analytics System is a platform designed for the organization and automation of policy management across devices and applications. The tool is intended for IT professionals to manage the various NetScaler products from a single dashboard. The platform also provides real-time analytics.
Entrepreneur Michel K. Susai founded NetScaler in 1997 in San Jose, California. He created NetScaler as a solution for reducing infrastructure during the growth of the Internet in the late 1990s. The company repositioned NetScaler as a security and optimization tool in 2001.  
By 2005, NetScaler estimated 75 percent of Internet users used its systems through clients including Google and Amazon. Citrix acquired NetScaler in 2005 for approximately $300 million in cash and stock.
In 2016, Citrix transitioned all of its delivery products under the NetScaler brand. Citrix CloudBridge SD-WAN became NetScaler SD-WAN. The company also introduced “NetScaler Management and Analytics System”, a console for users to manage all NetScaler products, including the ADCs and SD-WAN, and a containerized version of NetScaler called NetScaler CPX. Citrix released a free developer version of NetScaler CPX called NetScaler CPX Express in August 2016.
Reviewing NetScaler ADC in 2007, InfoWorld gave it a score of 8.6 out of 10. The reviewer noted that it was easy to set up and administer, and provided performance improvements in load balancing and Web application speed. However, there were variable results with features such as TCP session buffering and TCP session consolidation, as these would depend on other factors. As well, InfoWorld said that NetScaler is best suited for "organizations making corporate applications available over the Web for internal or external customers" and "large, heavily trafficked Web sites" but was more costly than other available solutions for a "small, three-node Web farm that will be lightly loaded".
GCN wrote in 2011 that NetScaler is "much more than a load balancer; it’s really an all-in-one Web application delivery system". The site gave NetScaler an A+ rating for features, B- for ease of use, A+ for performance and a C for value. The same article noted that it was difficult to learn and expensive.
In December 2019 a security problem was detected 
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- An issue was discovered in Citrix Application Delivery Controller (ADC) and Gateway 10.5, 11.1, 12.0, 12.1, and 13.0. They allow Directory Traversal.