How can I make taxonomies selectable via checkboxes?

Default categories for example in the blog post type are easily selectable in the backend via checkboxes and all available options are visible to the editor.

When creating custom taxonomies, however, the default interface is an input field. You may see the most used taxonomies as an editor, but you cannot see all of them, thus have to know which taxonomies exist.

There is, however, an easy workaround with which you can get the checkbox interface also for your custom taxonomies. When creating your custom post type or taxonomy, select "hierarchical".

You will then not only be able to create sub-categories, but you will also automatically have the checkbox interface instead of the input field.