How can I check if a plugin is installed and enabled? As the title suggests, I was wondering how to check if a certain plugin exists (and has been installed). 

And secondly, check that the plugin is actually enabled.

Thanks, 

Mark
On top of checking within the admin area, there are some other ways you can do this, both in templates and in your plugins.

In a template

{# Second argument is if you want enabled only #}
{% set plugin = craft.plugins.getPlugin('pluginHandle', false) %}

{# Now you have access to these methods... #}
{{ plugin.isEnabled() }}
{{ plugin.isInstalled() }}


For a full list of methods, see PluginVariable in craft docs.

For more info on how to get plugins within your templates, see the PluginsVariable, note this is different from PluginVariable.

In your plugin

To check a plugin from within your own plugin:

// Again, second arg is if you just want enabled plugins
$plugin = craft()-&gt;plugins-&gt;getPlugin('pluginHandle', false);

// Then you can do things like:
$plugin-&gt;isInstalled
$plugin-&gt;isEnabled;


See the PluginService and also the BasePlugin for more info.

Hope that helps :)