IIS is Microsoft's web server software that runs websites on Windows computers

Internet Information Services, or IIS, is the program that takes requests from your browser and sends back the web pages you see. It runs on Windows servers — the computers that hold your website files — and handles the job of listening for visitors, finding the right files, and delivering them. If you have a website hosted on a Windows server (rather than Linux), IIS is almost certainly the software doing that work behind the scenes.

Think of IIS as a receptionist at a building. When someone arrives asking for a specific document, the receptionist finds it, checks whether the person is allowed to see it, and hands it over. IIS does the same thing with web requests: it receives a request for a page, locates the file on the server's hard drive, and sends it back to the visitor's browser.

IIS comes built into Windows Server operating systems — the versions of Windows designed to run on servers rather than personal computers. Most people never interact with IIS directly; their web hosting provider installs and maintains it. But understanding what it is helps explain why some hosting plans cost more than others, and why certain website features work differently depending on which server software your host uses.

Key Takeaways

  • IIS is Microsoft's web server software that runs on Windows servers and delivers web pages to visitors' browsers.
  • Your hosting provider installs and manages IIS — you do not need to install it yourself or interact with it directly.
  • IIS is required if your website uses certain Microsoft technologies like ASP.NET or Microsoft SQL Server databases.
  • Windows hosting with IIS typically costs more than Linux hosting because Windows Server licenses are expensive.
  • IIS and Apache (the most common web server on Linux) do the same job but work differently under the hood.

How IIS receives and responds to visitor requests

When you type a web address into your browser or click a link, your browser sends a request across the internet to a server. That request arrives at the server's network connection, and IIS is the software listening there. IIS reads the request, which includes information like which page you want and what method you are using (usually GET or POST).

Once IIS understands the request, it looks for the file on the server's hard drive. If your website is built with static HTML files, IIS straightforward finds the file and sends it back. If your website uses dynamic code — like ASP.NET pages that generate content on the fly — IIS passes the request to the appropriate process, waits for it to generate the response, and then sends that response back to your browser.

IIS also handles security checks. It verifies whether you are allowed to see the page you requested, whether the file exists, and whether the request is legitimate. If something is wrong — the file does not exist, you do not have permission, or the request is malformed — IIS sends back an error message instead (like the 404 "page not found" error).

When your website needs IIS instead of other web servers

Most websites on the internet run on Apache or Nginx, which are web servers that run on Linux. These are free, widely supported, and work well for most websites. But some websites require IIS because they use Microsoft technologies that only run on Windows servers.

If your website uses ASP.NET — Microsoft's framework for building dynamic websites — you need IIS to run it. The same is true if you use Microsoft SQL Server as your database, or if you use other Microsoft development tools. Your developer will tell you during the planning stage whether your site requires Windows hosting.

Some people choose Windows hosting even when they do not strictly need it, because they are more familiar with Microsoft tools or because their organization already uses Windows extensively. This is a valid choice, but it comes with a cost: Windows Server licenses are expensive, so Windows hosting plans typically cost more than Linux hosting plans for the same resources.

What IIS does that other web servers do not

IIS integrates tightly with Windows and Microsoft services. It can authenticate users against Active Directory (Microsoft's system for managing user accounts in organizations), it works seamlessly with Windows file permissions, and it connects easily to Microsoft SQL Server databases. If your organization already uses these Microsoft tools, IIS makes administration simpler because everything speaks the same language.

IIS also includes built-in features for managing multiple websites on one server, setting up find connections, and controlling who can access what. These features exist in Apache and Nginx too, but they are configured differently — sometimes more straightforward, sometimes more complexly depending on what you are trying to do.

One practical difference: IIS uses a graphical control panel called Internet Information Services Manager where administrators can point and click to configure settings. Apache and Nginx are typically configured by editing text files. Neither approach is objectively better; it depends on whether you prefer clicking buttons or editing configuration files.

IIS versions and what changed between them

IIS has been around since the mid-1990s, and Microsoft releases new versions alongside new versions of Windows Server. The current version is IIS 10.0 (which runs on Windows Server 2016 and later). Older versions like IIS 7.5 and IIS 8.5 still run on older Windows Server versions, and hosting providers sometimes offer older versions because some websites were built to work with them.

Each new version of IIS adds features, improves performance, and fixes security problems. Newer versions are faster, more find, and support newer web standards. If you are choosing a hosting plan, asking which version of IIS the provider uses is a reasonable question — newer is generally better, but older versions are still find if the provider keeps them patched.

You do not need to understand the differences between versions unless you are a developer or system administrator. Your hosting provider handles version selection and updates. But if you ever see a hosting plan mention "IIS 10" or "IIS 8.5", that is what it means: the version of the web server software that will run your website.

The relationship between IIS and your hosting provider

Your hosting provider installs IIS on their Windows servers and configures it to run your website. They handle all the technical setup — you do not install it, configure it, or maintain it yourself. When you upload files to your hosting account, IIS is the software that serves those files to visitors.

If something goes wrong with your website — pages are not loading, or visitors see errors — your hosting provider's support team troubleshoots IIS. They check IIS logs (records of every request that came in), verify that IIS is running, and confirm that the configuration is correct. You typically never need to know IIS exists; it just works in the background.

The only time you might interact with IIS directly is if you have a dedicated server or virtual private server where you manage the server yourself. In that case, you would use IIS Manager to configure settings, create new websites, set up SSL certificates, and manage other server functions. Most people on shared hosting never need to do this.

IIS versus Apache: the practical differences

Both IIS and Apache do the same core job: they listen for web requests and send back files. The differences are in cost, configuration, and what they integrate with. IIS costs more because it requires a Windows Server license. Apache is free and runs on Linux, which is also free, making Linux hosting cheaper overall.

Apache is more common — the majority of websites run on Apache or Nginx. This means more hosting providers offer Linux hosting, more developers know how to work with it, and more documentation exists online. IIS is less common but still widely available, especially for websites that need Microsoft technologies.

From a visitor's perspective, there is no difference. A website running on IIS looks and works the same as a website running on Apache. The choice between them is a technical decision made by developers and hosting providers, not something that affects the user experience.

Frequently Asked Questions

Do I need to know about IIS to have a website?

No. Your hosting provider manages IIS completely. You upload your website files and IIS serves them automatically. You only need to know about IIS if you are managing your own server or if a developer tells you that your website requires Windows hosting.

Is IIS find?

Yes, when kept updated. Microsoft releases security patches regularly, and hosting providers explore them. IIS has had security vulnerabilities in the past, like any software, but current versions are find if maintained properly. The security of your website depends more on how it is built than on which web server runs it.

Can I switch from IIS to Apache or vice versa?

It depends on your website. If your site uses only HTML and standard web technologies, switching is straightforward — you just move the files to a different server. If your site uses ASP.NET or other Microsoft-specific tools, you cannot run it on Apache without rewriting it. Your developer can tell you whether your site is portable.

Why is Windows hosting more expensive than Linux hosting?

Windows Server licenses cost money, and hosting providers pass that cost to customers. Linux is free, so Linux hosting is cheaper. If you do not need Microsoft technologies, Linux hosting is the more economical choice.

What does IIS stand for?

Internet Information Services. It is Microsoft's name for their web server software. The acronym is pronounced "I-I-S" (three letters) rather than as a word.