Inflation, an era of accelerated expansion of our universe prior to the radiation phase, constitutes the paradigm of primordial cosmology, and I will review its foundations as well as the observational tests it has passed.
However, our microphysical understanding of inflation is still limited, and embedding it into realistic high-energy physics frameworks is challenging. I will describe these theoretical challenges, recent progress in this field, as well as how ongoing and future observations will help us to pinpoint the physics active in the very early universe.