Abstract: I will explain a series of my works that has resulted in the first ever construction of a controlled cosmological solution of string theory in which the vacuum energy — though negative in sign — is exponentially small, while extra dimensions are microscopic. I will also, in brief terms, outline some of my ongoing efforts to construct solutions with positive vacuum energy. Finally, I will turn to another series of my works about probing string theoretic axions — the string axiverse. I will argue that the strong CP problem is generically absent in string compactifications, and that future observation might well detect string theoretic axions through their couplings to photons.