The conference "de Sitter and microstate lansdscapes in string theory" took place at IPhT from June 16 to 19, 2015. This workshop gathered 70 participants from around the world to discuss recent advances in understanding the landscapes of de Sitter spaces in string theory on one hand, and of black hole microstate geometries on the other. Both landscapes have experienced quite intense recent remodeling: on the black hole side this was driven by “fuzzball/firewall” information-theory-based arguments that black hole solutions are only thermodynamic approximations that stop describing the physics at the scale of the horizon, where they should be replaced by horizonless geometries dual to the black hole microstates, and on the cosmology side by the realization that antibranes, which are one of the key ingredients needed to obtain a landscape of de Sitter vacua, may give rise to instabilities.