The Eridanus supervoid is an enormous underdensity in the galaxy distribution spanning approximately 250-300 million light-years, located in the direction of the constellation Eridanus. This structure is problematic for Lambda-CDM because such extreme underdensities are statistically improbable in a universe starting from Gaussian random density fluctuations as predicted by inflation. The supervoid's existence and properties suggest either that the initial conditions of the universe were not Gaussian random, or that structure formation and void generation operate differently than standard models predict. The size and emptiness of the Eridanus supervoid strain the assumptions of homogeneity and structure growth rates central to Lambda-CDM cosmology (Granett et al. 2010; Keenan et al. 2013).