The Satipatthana Sutta (usually translated as the Foundations of Mindfulness) offers a complete description of the practice of mindfulness, beginning with the direct awareness of the breath and the body, progressing through mindfulness of vedana or feeling tone, to the more subtle object of the Third Foundation, mindfulness of mind states. The Fourth Foundation of Mindfulness represents the culmination of this series of practices, and can be seen as a direct pointing, again and again, to the possibility of freedom through direct awareness of where we get caught, and how to turn the mind towards liberation. This talk is an overview of the practices of the Fourth Foundation, which can be seen as both the last in the sequence of practices, and as a progression in itself. It also covers how the Fourth Foundation can be skillfully interwoven into our practice of the other foundations.