At first sight, the Large Hadron Collider (LHC) and Early Universe Cosmology have little in common, probing respectively the smallest and largest scales in nature. Nevertheless, one of the greatest successes of modern physics has been to demonstrate the deep connections between the two fields: The properties of fundamental particles affect the evolution of the early universe, and many models that modify cosmological observables can be tested at colliders. In my talk, I will illustrate this connection with three specific examples. First, I will demonstrate that searches for long-lived particles at the LHC can probe models that modify the expansion rate of the universe through non-thermal dark radiation. Second, I will show that early universe structure formation points towards self-interacting dark matter particles, which may give rise to highly unusual collider signatures. Finally, I will discuss how a global analysis of LHC searches may help us pin down the properties of dark matter particles.