Qualys, Inc. is a provider of cloud security, compliance and related services for small and medium-sized businesses, as well as large corporations based in Redwood Shores, California. Founded in 1999, Qualys was the first company to deliver vulnerability management solutions as applications through the web using a "software as a service" (SaaS) model, and as of 2013 Gartner Group for the fifth time gave Qualys a "Strong Positive" rating for these services. It has added cloud-based compliance and web application security offerings.

Qualys has over 9,300 customers in more than 100 countries, including a majority of the Forbes Global 100. The company has strategic partnerships with major managed services providers and consulting organizations including BT, Dell SecureWorks, Fujitsu, IBM, NTT, Symantec, Verizon, and Wipro. The company is also a founding member of the Cloud Security Alliance (CSA).

Qualys was founded in 1999. The company launched QualysGuard in December 2000, making Qualys one of the first entrants in the vulnerability management market. The QualysGuard Intranet Scanner was released in 2002 to automatically scan corporate LANs for vulnerabilities and search for an available patch. The following year, Qualys released FreeMap, a web-based tool for scanning, mapping and identifying possible security holes within networks connected to the Internet.

In 2005, Qualys extended its QualysGuard product line. In 2008, Qualys introduced QualysGuard Policy Compliance, which extended the platform’s global scanning capabilities to collect IT compliance data across the organization and map this information into policies to document compliance for auditing purposes. Qualys also released a service for web application scanning named QualysGuard Web Application Scanning (WAS). In 2010, at the RSA Conference USA, Qualys announced QualysGuard Malware Detection Service, a new service designed to scan and identify malware on web sites. It also announced the Qualys SECURE Seal, which allows websites to show visitors that it has passed security scans.

In July 2010, Qualys announced Qualys BrowserCheck, a service for checking web browsers and plug-ins for security vulnerabilities. At RSA Conference 2011, Qualys launched a new open source web application firewall project, IronBee, led by Ivan Ristic, the creator of ModSecurity and a director of engineering at Qualys. At the RSA Conference in 2012, Qualys introduced updates to the QualysGuard Cloud Platform, which extended its capabilities to help customers improve the security of their IT systems and applications, further automate their compliance initiatives for IT-GRC, and provide online protection against cyber-attacks while reducing operational costs and increasing the efficiency of their security programs.

Qualys went public on NASDAQ with the symbol QLYS on September 28, 2012, raising net proceeds of $87.5 million. At the 2014 RSA Conference, Qualys announced general availability of its QualyGuard Web Application Firewall (WAF), which provides protection for websites running on Amazon EC2 and on-premises, as well as a new Continuous Monitoring solution and free Top 4 Security Controls service. In 2015, the company released 2.0 of its WAF software which included virtual patching and customizable event responses. That same year, Qualys also released an IT security and compliance solution called Cloud Agent Platform. In August 2015, the company released a free asset management service, Qualys AssetView, that allowed organizations to keep inventory of computers and their software.

In February 2016, Qualys released ThreatPROTECT, a vulnerability detection service for its cloud-based platform.The company received full certification for its Configuration Management Databases (CMDBs) App for ServiceNow, allowing the app to be integrated into ServiceNow's system in March 2016. In July 2016, it was announced that Qualys would integrate with Microsoft Azure Security Center. In August 2017, Qualys acquired the network analysis assets from Nevis Networks for an undisclosed sum.

SC Magazine has awarded Qualys for its security software solutions every year from 2004-2014. SC Magazine also awarded Qualys "Best Security Company" in 2014.

In 2010, Inc. magazine ranked Qualys within 5000 fastest growing private companies in the USA based on 104% revenue growth from 2006 to 2009. In 2012 Silicon Valley/San Jose Business Journal has recognized Qualys as one of the largest private companies in Silicon Valley – ranking 26th in a list of 51.

In November 2014, Qualys received the 2014 Security Reader's Choice Awards for Best Risk and Policy Compliance Solution, Best Application Security Product, and Best Vulnerability.

In both 2014 and 2015, Qualys received the award for Best Application Security Product from the SANS Institute.