Since the invention of the Er-doped optical amplifier a decade ago, commercial optical fiber communication systems have increased in transmission capacity by almost four orders of magnitude. This increase has been made possible by eliminating the repeaters that previously regenerated optical signals every 20 km and by the advent of WDM (wavelength division multiplexing) in which a large number of wavelength channels are used to simultaneously transmit information. In modern-day systems, information remains in an all- optical format for about 500 km in terrestrial systems and up to 6000 km in undersea systems. With the advent of optical networks, these distances are only likely to grow. Given the complexity and cost of modern-day optical communication systems, accurate design modeling of optical fiber transmission has become absolutely necessary, and most major telecommunication companies now devote significant efforts to it. My own research group has been at the forefront of developing new methods and algorithms to meet this need. The key physical effects that must be modeled include nonlinearity, chromatic dispersion, polarization effects, and amplified spontaneous emission noise from the amplifiers. Recent advances that my group has made include: (1) Development of the Manakov-PMD equation as the fundamental equation describing optical fiber transmission including polarization effects and development of the coarse step method that allows its rapid and accurate solution, (2) development of the mean field approach that allows the user to accurately model many-channel WDM systems while only keeping a small number of channels, and (3) development of linearization approaches that allow the user to accurately model the effects of amplified spontaneous emission noise without the use of numerically time-consuming Monte Carlo simulations. These and related developments will be described.