Anatomy of a Portlet

The bits that go to make up a portlet renderer (which is the bit of a portlet you'll want to customize).

Customizing a portlet is similar to overriding a viewlet, but rather more straightforward. There is a specific ZCML directive for customization.

Directive in ZCML

<plone:portletRenderer />

Attributes in ZCML

a marker interface for your particular theme
the interface of the portlet you wish to customize
location of the template you wish to override
your custom class (use this if you don't specify a template) for rendering the portlet