Systems allowing controllable photon-atom interactions are becoming increasingly important for quantum communication applications. One promising platform involves the interaction of the tightly-confined evanescent mode of an optical nanofiber with surrounding atoms. This dissertation will overview our work on the interaction of nanofiber-guided light with a warm rubidium vapor. In comparison to related work with cold atom clouds or trapped atoms, the "warm atom-nanofiber" system is fairly robust but operates in a regime where motional effects of the atoms are significant. We will first discuss a detailed study of saturated absorption in this system, with an emphasis on the role of motional effects in hyperfine pumping rates and various line broadening mechanisms. The power needed to saturate the system is essentially a measure of the system?s capability to enable nonlinear optical interactions of the kind that are needed for quantum communication applications, and we observe remarkably ultralow saturation powers of 10?s of nW (corresponding to only ?10 photons passing through the nanofiber at a given time). We then utilize this strong nonlinearity to demonstrate 3-level ladder-type electromagnetically induced transparency (EIT) and all-optical modulation with ultralow control-field powers on the order of only a few ?W. Finally, we discuss a novel nanofiber-segment nonlinear ring resonator comprised of a large loop of conventional single-mode fiber with a short nanofiber segment surrounded by a warm rubidium vapor. In this device, the cavity enhanced evanescent field of the nanofiber enables even stronger photon-atom interactions.