Multimode nonlinear fiber optics is a microcosm, a hyperspace of possibilities embedded within a niche of a niche of science. It is full of phenomena that transcend dimensionality (these provocative statements will be clarified). It could inform new generations of compact, cost-efficient scientific tools, or major upgrades to optical fiber telecommunications. These advances in foundational, infrastructural technologies would have major impact on the human world, from science and knowledge through to the economic engine of the internet.

In this thesis, I examine the work of my PhD that has explored nonlinear pulse propagation in multimode fibers. Both as a microcosm of science, a mostly-mundane story of half-reasoned exploration, and as a rich and complex world of observed phenomena and inspired applications, here I attempt to retrospectively describe the work and science in as coherent a summary form as can be managed at this point. We examine first multimode solitons in anomalous dispersion fibers. These are stable configurations of light in nonlinear multimode fiber and, in some sense, the conceptual building blocks or framework through which we can understand much more complex dynamics of multimode supercontinuum generation. We then examine the complex mode coupling in nonlinear, disordered multimode fibers, and attempt to integrate the multitude of effects into a cohesive framework of modal energy flow. Finally, we explore multimode fiber lasers and spatiotemporal mode-locking, the most general form of coherent light self-organization in an optical oscillator.