Inflation is an epoch in the very early universe, characterised by a nearly exponential expansion. It provides an explanation for the origin of cosmic structure and it is in excellent agreement with current observations. The particle physics description of inflation is, however, still largely unknown. Primordial gravitational waves have the potential to shed new light on this epoch. In this talk I will discuss gravitational wave production during inflation and highlight our future prospects for testing inflation using all available primordial gravitational wave probes, from the cosmic microwave background all the way to interferometers.