Django – what is the difference between render(), render_to_response() and direct_to_template()?

Whats the difference (in language a python/django noob can understand) in a view between render(), render_to_response() and direct_to_template()?

e.g. from Nathan Borror’s basic apps examples

def comment_edit(request, object_id, template_name="comments/edit.html"):
    comment = get_object_or_404(Comment, pk=object_id, user=request.user)
    # ...
    return render(request, template_name, {
        'form': form,
        'comment': comment,
    })

But I’ve also seen

    return render_to_response(template_name, my_data_dictionary,
              context_instance=RequestContext(request))

And

    return direct_to_template(request, template_name, my_data_dictionary)

Whats the difference, what to use in any particular situation?