As the hunt for the elusive dark matter (DM) progresses, an impressive series of null results has severely limited options for DM that freezes out via standard model interactions. A hidden sector containing the dark matter and a mediator particle provides a minimal alternative origin for DM. If the mediator is heavier than the dark matter, the dark matter must freezeout into standard model particles, requiring a sufficiently strong connection between the two sectors. If the mediator is lighter than the dark matter, it can freezeout independently of the sector's very weak connection to the standard model fields, opening opportunities for phenomenology. I will discuss these minimal simplified models for hidden sectors, before focusing on two cases, hidden sector freezeout (the WIMP next door) and its out-of-equilibrium continuation, leak-in. I will discuss constraints from a wide array of complementary experimental approaches, the leak-in mechanism, and address how the features of these models survive in extensions beyond the minimal case.