This thesis is a study in theoretical cosmology with an emphasis on the high-redshift universe and promising directions for future observations. In Chapters 2 and 3, we propose intensity mapping of spectral line emission from galaxies. This is a technique to observe the cumulative emission from many galaxies without resolving individual sources. We use analytic calculations and N-body simulations to predict the observational signal for different emission lines, including those from oxygen, carbon monoxide, and carbon.
