My dissertation describes experiments on two-photon excitation of ultracold Sr to the 3S1 Rydberg series and represents the first experiments exciting Rydberg atoms via an intermediate triplet excited state. Due to the narrow linewidth (7.5 kHz) of the 1S0 – 3P1 transition in Sr, this excitation scheme yields longer coherence times and less loss from the intermediate state compared to methods using the usual dipole allowed transitions. This is advantageous for realizing the possibility of Rydberg dressing, where a small amount of Rydberg character is admixed to ground state atoms allowing for continuously tunable long-range interactions. With this goal in mind, we explore the interplay of Rydberg blockade, Rydberg-Rydberg interactions, and ground-Rydberg interactions in high density, ultracold gases through Autler-Townes spectroscopy and photoassociation of ultralong-range Rydberg molecules.