How can Twitter Bootstrap 3 be integrated into Symfony 2 for CSS/JS usage?

To integrate Twitter Bootstrap 3 into Symfony 2 for CSS/JS usage, you can use Assetic to manage your assets. First, download Bootstrap and place the files in your Symfony project's web directory. Then, configure Assetic in your Symfony configuration file to include the Bootstrap CSS and JS files in your templates.

// app/config/config.yml

assetic:
    assets:
        bootstrap_css:
            inputs:
                - '%kernel.root_dir%/../web/bootstrap/css/bootstrap.min.css'
        bootstrap_js:
            inputs:
                - '%kernel.root_dir%/../web/bootstrap/js/bootstrap.min.js'
```

In your Twig templates, include the Bootstrap assets using Assetic's `stylesheets` and `javascripts` functions:

```twig
{# app/Resources/views/base.html.twig #}

{% block stylesheets %}
    {% stylesheets '@bootstrap_css' %}
        <link rel="stylesheet" href="{{ asset_url }}" />
    {% endstylesheets %}
{% endblock %}

{% block javascripts %}
    {% javascripts '@bootstrap_js' %}
        <script src="{{ asset_url }}"></script>
    {% endjavascripts %}
{% endblock %}