WordPress Multisite overview

WordPress Multisite, historically known as WordPress Multi-User or WPMU, lets one WordPress installation manage several related sites through a single dashboard, content pool, and database. It is not a separate product: it is a network mode switched on in a normal WordPress install. It helps when you run several sites that share the same code, plugins, themes, and admin identity.

What it is

A Multisite network has one main installation and a network admin who oversees all the sites. Each subsite gets its own URL, content, users, and plugins that can be activated, but the core software, database schema, and the network-level plugins and themes are shared and maintained in one place.

The trade-off follows directly. The single shared codebase means one update covers everything and you administer many sites at once, which is the appeal. The cost is that sites share tables and plugins, so a network problem or a risky plugin affects every site, and some plugins and hosts do not support network mode. Maintenance is centralised, but independence is reduced.

Subdomain or subdirectory

The first decision is the URL structure of the network, and it cannot be changed trivially later, so it deserves care.

• Subdomain mode uses URLs such as site1.example.com. It needs wildcard DNS for on-demand subdomain creation, and each site normally needs a certificate covering its subdomain, often a wildcard certificate. It suits sites that should be distinct, such as regional or brand sites with separate audiences.
• Subdirectory mode uses URLs such as example.com/site1. It needs no wildcard DNS and no extra certificates, because all sites share the same domain. It works well for same-brand properties such as a blog, a store, and a knowledge base.

The main installation must live at the domain root to choose subdomain mode, and a subdirectory network cannot be chosen if the existing site has been running for a long time because of permalink issues. Verify both constraints before committing.

Setup and when to use it

To enable a network, add the following above the "stop editing" marker in wp-config.php:

define( 'WP_ALLOW_MULTISITE', true );

After the installation screen completes, WordPress writes network constants to wp-config.php and rules to .htaccess, which you must add. From then on the Tools > Network admin area manages sites, plugins, and users across the whole network.

Reach for Multisite when the sites truly share code and maintenance, for example distinct public-facing properties of one brand that need one login and one update cycle. Avoid it when sites have different owners, very different plugin needs, or strict isolation, because a single shared base is the wrong fit for independence and can create exactly the kind of cross-site blast radius that breaks unrelated sites. For orthogonal cases the safer modern choice is separate installations managed by a tool such as WP-CLI. See WP-CLI scaffold for managing several independent sites on the command line.